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Introduction - TECFA - Université de Genève

1. Customer Account 1 i abstract income double m palance double credit double PAT EEN T checkWithdrawLimit double checkWithdraw Limit 0 CurrentAccount Private Account checkWithdraw Limit double checkWithdraw Limit double SavingsAccount checkWithdraw Limit double Fig 5 the account example Avoid using static constants static final to define limits for withdrawal or overdrawing You may do so later on when teaching the relationship be tween types and class variables But when you teach inheritance poly morphism and the overwriting of methods then your students encounter already enough new information In the account framework above you can demonstrate a useful polymor phism by programming checkWithdraw Limit in class customer You 25 7 2 Chapter 3 Key problems of teaching object oriented programming should get the overall limit from all accounts of the customer You must refer to the accounts by an array or by a collection Vector for in stance Later one may even use an interface creditable with operations like checkW ithdraw Limit Before you have such an interface checkWith draw Limit is only realised in class customer Afterwards it is a type You may demonstrate that you can mix customers and accounts for in stance in an array of type creditable to get
2. if system Windows3 drawWindows3Button j if system Windows95 drawWindows95Button In an object oriented program we would have a module a object as server that provides us the objects of the user interface In the beginning we would activate this server userInterface new Windows95UserInterface Interface is now the reference to these objects that serve as elements of the user interface Now all we have to do is ask this server to provide us with elements of the user interface if system if system 13 3 2 3 3 3 4 Chapter 2 Paradigm shift to object oriented programming userlInterface draw Button The server userlnterface draws for us the button On Windows 95 a windows 95 button The code inside of the server does only treat Win dows 95 buttons There is no need for conditional branching Recursion There is no need to discuss recursion in object oriented programming If the instances of a class do their job correctly they will do it also when called recursively For instance In the composite component design pat tern any container calls all its components As every container is also a component this is a recursive call Studying this design patterns that has a recursive structure association replaces the analysis of recursive pro cedure calls The composite component design pattern is discussed in Gamma e a 1994 The expression recursive call
3. Customer MonthlySalary Fig 2 objects as server and client The information exchanged between server and client is not directly re lated to the internal data in the server For instance a server asked to provide the monthly salary could return the average income of the last three years in case of a salesman with a volatile income or return a value set by the customers contact person in case of an important customer in private banking There is no need to enter wrong numbers into fields just to work around inflexible data structures The data structure must be flexible whereas the messages sent to the server do not change Therefore the strategy is to define the services provided by any element of the application the responsibility of the classes and which classes should interact with each other the collaboration For the services that the class should provide methods are written The methods either check the information inside the class and give an informa tion query methods or that change the information inside the class up date methods Usually when the most basic methods are written firstly there shouldn t be any complicated methods That means after having defined classes responsibilities and collaborations writing methods is ba sically a bottom up strategy 12 Chapter 2 Paradigm shift to object oriented programming 3 Key Concepts Compared 3 1 Procedural programming and obj
4. 12 2 Cognitive Level and Cognitive Load Such multiple choice questions are training on a high cognitive level The trainee has to apply his knowledge to a new situation The extrinsic cogni tive load is low because attention is not splitted as much as it would be in an online training situation Plus in online training several steps are needed to get feedback Often the trainee has to ask for support to get an accurate feedback For instance because the code above did not what he has expected it to do The effectiveness of this approach gives some support to cognitive load theory But especially to this approach there are other theories that apply as well This kind of multiple choice questions is derived from behavioural psychology It is known as Discrimination Frame Sequence Espich 1967 p 38 12 3 Similar Check Up Questions In a live educational setting you can implement this kind of multiple choice trainings in various ways Dorig and Waibel explain the group ac tivities below in Dorig 1995 There are group activities that use discrimi nation Multiple choice questions can also be used for flash cards 12 4 Group Activity Imperator You can give short code examples to the trainees and ask them to decide whether it compiles or not whether it creates the output you want or not In a group of youngsters it is highly appreciated to decide yes or no by thumb up and down The trainer or moderator asks the questions and a
5. got another meaning in object oriented programming See Object Modeling Group 2000 3 60 2 It means that the object calls itself and not that a method calls itself The later is only a very rare and unimportant sub case of the first Also when taking a closer look at other books discussions on recursion are rare Eckel s object oriented programming bible Thinking in J ava Eckel 1998 mentions recursive method calls only twice on page 342 as something causing a never ending loop and on page 926 he uses it and explains it by the way Sun s J ava Tutorial does not mention recursion other authors just men tion it shortly giving one example for instance Schildt 2001 p 246 Modularisation Obviously this cannot be any topic in object oriented programming be cause classes are already small modules Instead of modularisation ob ject oriented programming uses packaging to produce units that could be regarded as parts of a larger application Side Effects Avoiding side effects and handling the procedure s parameters with care is a major topic in a course for procedural programming Therefore how to avoid side effects is a major topic in a good book or course about proce dural programming Side effects in object oriented programming are very rare and can easily be avoided The increment operator has a side effect when put in front of the variable Then the variable returns the incremented number Example i O while
6. 16 Listener waitForUser p beeper beeperGetted gt turnLeft ee lt c return beeper beeperGetted gt turnLeft lt q _ return Fig 27 sender 2 listeners as sequence diagram 93 Chapter 8 Supporting the Unified Modelling Language Also in the case of sequence diagrams after some training students may write down the interaction they expect with a sequence diagram and ver ify whether their expectations are met 2 5 Statechart Diagrams Even as worlds are simple they still are rich There is inheritance and ag gregation Talking about statechart diagrams there are very interesting states A full statechart diagram could look like the figure below new Operating facing occupied cell Blocked do turnLeft Empty On beeper cell facing free cell pickBeeper beeper facing occupied putBeeper cell Free Loaded beeper cell ahed do move move do turnLeft facing free cell carring two or more beepers putBeepe j i i f i j j i i i l i i carring one ij i i l i i I i I i i destroy Fig 28 statechart diagram of a robot would strongly recommend to analyse this concurrent states individually in the beginning and to compile them to one diagram later in the course whe
7. The draw back of this idea is that you are switching the learning environ ment twice From Karel to J Karel from J Karel to regular J ava decided to start a new world because had some additional ideas for improvements 68 Chapter 6 Reducing cognitive load in Roboworld As decided to design a new microworld Roboworld to overcome disad vantages of the existing once considered also reducing cognitive load even more than the existing worlds do Everything that distracts students from learning should be omitted while maintain compatibility to the pro gramming language J ava What this world should provide to lower cognitive load 1 Hassle Free File Handling 1 1 Existing worlds use open and save actions for scenarios and for classes The advantage of this is flexibility the disadvantage is that there is no list of scenarios A list of scenarios lets users quickly switch scenarios and gives them an overview Advantages A trainee might like to look up a scenario to examine classes he has writ ten there A list of scenarios helps him to find the scenario Retrieving a file from the file system is more cumbersome 7 Foy Hir m Wald of Robota Manage Sen Fig 15 List of scenarios will be listed alphabetically in the final version Retrieving files might also add to cognitive load if the trainee is not abso lutely familiar with file handling procedures Quickly browsing scenarios is not possi
8. Wilson 1995 chapter Cognitive Load Theory A Crossover Theory of Learning and Instruction writes referring to cognitive load theory These instructional prescriptions are consistent in spirit with traditional instructional theories Because they come from a cognitive psychologist however they are tightly coupled with a specific learning theory Conceivably they could conceivably be taught to designers as rote rules to apply 3 1 Cognitive Load Theory as Rote Rules to Apply The question is whether cognitive load theory is a powerful tool to analyse existing problems in a field like object oriented programming and helps to locate and improve the best means to overcome these problems There is some existing evidence that a theory like cognitive load theory should be powerful Cognitive load theory has a view understandable rules The practitioner should be able to estimate the number of schemata in some part of his course or in his instructional material So he can locate prob lems caused by cognitive load He can think whether he may build up higher level schema as prerequisites of this unit or to split the unit He can check for additional cognitive load caused by the instructional material 3 2 Simplicity of the Theory Is its Strength Studies done in Germany in the early 70ties prove how important the sim plicity of a method is if the goal is improvement in the practical field Langer e a 1981 did comprehensive resea
9. e sur une coordination de registres donne ces possibilit s de transfert Translation An understanding based only on one sign system is an understanding that allows no transfer at all Only an inte grative understanding this means an understanding based on the coordination of sign systems makes transfer possible This conclusions is also supported by the review of Iding 1997 p 249 for the usage of analogies to understand technical writings See A Effectiveness of Metaphors b To conclude the Unified Modelling Language as believe is inevitable for two reasons Firstly it is used for communication in books among devel opers in classroom for documentation see for instance Beck 2000 Secondly it is needed by the student himself as soon as he or she starts to design and implement more complex structures There will be almost no chance to transfer the knowledge to this new situations if students do not have an integrated understanding of the paradigm of object oriented pro gramming in different sign systems and are able to switch from the one to the other Conclusion Students can use the Unified Modelling Language for communication for personal notes and to build an integrated understanding of object oriented programming in different sign systems As design patterns help to reduce cognitive load dramatically when studying the API for instance the parts to set up the graphical user interface with Swing or AWT or input
10. i lt 10 fiestas aad eo where a side effect occurs can be translated to i 1 while i lt 10 eo i where there is no side effect The student sees that the loop starts with 1 and does not need to figure out whether it starts with 0 or with 1 The easiest way to reduce cognitive load here is just not to mention the first possibility for an increment 14 Chapter 2 Paradigm shift to object oriented programming Eckel 1998 chapter A Passing amp Returning Objects writes about real side effects ln general you call a method in order to produce a return value and or a change of state in the object that the method is called for A method is how you send a message to that ob ject It s much less common to call a method in order to ma nipulate its arguments this is referred to as calling a method for its side effects Thus when you create a method that modifies its arguments the user must be clearly instructed and warned about the use of that method and its potential sur prises Because of the confusion and pitfalls it s much better to avoid changing the argument Most Authors do not even mention real side effects in object oriented pro gramming 4 Novices Problems in Programming 4 1 4 2 Novices problems with procedural programming Lewis 1980 as reported by Rajan 1990 found for a procedural pro gramming language the following problems of novice program
11. true coachLicence false Fig 9 object diagram to the class diagram in fig 8 Analyse patterns with simple real live problems like customer account transaction showed to be preferable for exercises 45 Chapter 4 Existing solutions to overcome the problem of cognitive load 5 8 Examples and Exercises A teacher should provide examples that are easy to understand and use the same examples for all the different kinds of diagrams Good examples are not easy to find e The example of the different vehicles for instance works fine with static diagrams or even a statechart of a vehicle but it is rather ab stract when you are going to set up CRC Cards and test some program flow What is the responsibility of the wheel Which classes got the responsibility for a turn What is the program flow of a turn e Examples like a library or a bank work fine but need some understand ing of data handling and tend therefore to become too complex For trainees with a background in database programming such examples should work fine e We thought that simulations should work fine We worked out an ex ample with a washing machine But the example was not specific enough Therefore the trainees could not find a solution Games might be good examples have not tried this yet 5 9 At our Institution for Adult Education We Gave Up this Approach for Two Reasons 1 The feeling that the knowledge is too abstract for be
12. while and uses loop instead of the for statement and J Karel and the Hamster Model that are written in pure J ava Solution in the Spirit of Cognitive Load Awareness The solution of Karel using only three conditional branching control structures is the choice Avoiding the Switch statement is evident Once basic are learned there will be an example where the teacher can intro duce the Switch statement as an elegant way to use a Clear and easy code There is no need to introduce Switch early It even does not intro duce any schema One can easily substitute the Switch statement by nested If statements Also the For statement of J ava is always intelligibly replaceable by a While statement The For statement in its full power is redundant But looping a fixed number of times needs a quite complicated coding There fore introducing a Loop statement with a very simple code sounds sensi 79 Chapter 6 Reducing cognitive load in Roboworld ble It introduces a schema executing a fixed number of loops with a very simple code So even as there is no Loop statement outside of mi croworlds there is a loop schema that is used rather frequently 10 Feedback in Case of Never Ending Recursion 10 1 Motivation In the chapter were analysed differences between object oriented pro gramming and procedural programming stated that recursive procedure call is not a paradigm of object oriented programming also explained that exte
13. 3 teachers should explain how to map the analogy to the actual problem Sign systems and semiotic morphism are discussed more deeply in the section SBmiotic Research on Mathematical Sign Systems p My Personal Preference As there is no really evident metaphor authors follow their personal pref erences always use companies that provide services as metaphor for object oriented programming like in the doctor patient example of Bergin 2000 whereas old fashioned industries are a metaphor for procedural programming In companies that provide services there are always user client situations People are exchanging messages They keep their data at their work place Usually you do not use files directly from other people s desks You rather ask them to provide information Or to process a request based on the information they keep in their files or on their desks Em ployees have responsibilities and they are collaborating In procedural programming you have data before it is processed input basic or half fabricated material Then you process the data or material This process may be split up into sub processes At the end of the fabrica tion process you got the final material the processed data or output You are free to change the fabrication process But when you change input or output you are forced to rather large adaptations in the fabrication proc ess prefer these metaphors to show that procedural programming is n
14. Collaboration and encapsulation Working with object references or pointers 3 Inheritance and Polymorphism will analyse these problems in the following three sections 5 Miss Understanding Static Attributes and Operations 5 1 This is a small but nasty problem Because trainees mix up the concepts of classes and objects Plus ideas of overall control dominate their think ing Concentrating on objects can help introduce the notion of static object to clearly separate the concept of class and object Description of the Problem In object oriented programming we set up classes These classes define objects These objects shall do the job Therefore there is not much need for static operations and static attributes But in the beginning students need to store information sometimes and they want to retrieve this infor 20 Chapter 3 Key problems of teaching object oriented programming mation without worrying too much about the design of objects and their classes So this is what you will see Students use static attributes where you would expect object s attributes This occurs if there is only one object of a class in a specific project Students will defend themselves Well it works Firstly tried an objects attribute but then there appeared any compiler error tried the static attribute and it worked This means Students have not understood the process of instantiating an object They try to work with
15. Hamster Model gives a one line feed back about execution at the bottom of the window The visualization of Karel is more elaborated It uses the way debuggers show code execution Fig 20 Hamster Model 74 Chapter 6 Reducing cognitive load in Roboworld Fig 21 Feedback about execution in Karel Also feedback about execution is more sophisticated in Karel it works with splitted attention The attention goes back and forth between Karel in the right window and the sequential execution shown in the window to the left The window to the left with the code jumps up and down to dis play always the current line of code which will be executed next 75 Chapter 6 Reducing cognitive load in Roboworld 5 3 Improvement As the four graph ics show execu tion is displayed as messages between robots Calling is visualised by red colour returning by black colour The calling robot turns green to show that it is still running The inactive robot stays black There is no split attention and no inadequate usage of colours Fig 22 Sender and Listener exchanging messages This way the most information about the exchange of messages is where it ought to be on the graphic The trainee should be able to see every single step in the process A method call is not only the passing of control it is the passing of values too The return of the method is not only the passing of cont
16. Karel as soon as there is need for access modifiers 11 3 Operators Are Not Essential Operators as are not implemented Even without such operators one can do mathematical tasks like converting a binary number set by beepers for instance beeper beeper no beeper beeper in the decimal number 13 8 4 0 1 if there is some need to do mathematical exer 80 11 4 11 5 11 6 11 7 Chapter 6 Reducing cognitive load in Roboworld cises Another interesting but very demanding mathematical exercise would be to operate an abacus with beepers You can substitute Boolean operations by nested If statements Type Safety Type safety demands quite an overhead of knowledge How to define an interface declare implementation do the implementation use the In stanceof operator or understanding the error messages in case of type incompatibility Type safety is not needed because the trainee can realise types rather than defining them explicitly as interfaces and implement them In case of calling an operation that a robot does not realise he sees exactly when and why his or her application crashes So the goal is rather to experience the need for type safety than to work with the tools inter face implementation of type safety To conclude the teacher can introduce the schemata related to types For instance in the example of one sender and two listeners we could have two different classes of listener that both impleme
17. Setting a beeper is like clicking Setting a wall is like pressing a modifier key In the ae of sender listener Fig ler a J Inessages p 76 the user can add a beeper to the field where the sender is The sender checks for the beeper removes it and sends a message to the listener This example gives students not only a simple example of the sender listener concept used in J ava Swing or AWT but also a concrete idea how this sender listener concept might be implemented in the J ava runtime environment J RE 2 Objects Robots Operations Methods Classes 2 1 Robots stand for objects Is this a accurate metaphor Robots Are a Perfect Metaphor for Objects Robots are programmable in the real world and in the microworld There fore students are familiar with the idea of writing programs for a type of robot This means a class which is the written program for a type of ro bots seems to be an all natural idea There are different types of objects as there are different types of robots Also the behaviour of objects are defined in classes as the behaviour of robots is defined with them Robots and objects both store data internally Data that is lost when the robot or object is discarded Objects and robots both exchange messages i e call operations of other objects robots When a robot object receives a message a call to one of its operations it performs the method it has been trained pro grammed 85 2 2
18. The first uses 1 to 8 beepers The first colour means white the second black the next six beepers paint the colour circle red yellow green 84 1 4 Chapter 7 Explaining basic concepts with Robow orld blue magenta With this colour scheme students may be asked to do colour paintings or even write primitive drawing applications In such an application two robots may work together the first is responsible for a figure the second for the colour The second colour coding starts at the number of nine beepers Setting 9 beepers means black no light at all Adding one beeper means adding blue you return from complete blue to no blue adding 6 beepers means adding green you return from complete green to now green adding 36 beepers means adding red May be you recognize this as the 216 web colours coded with beepers This way you may visualise that different values can mean different out put depending on the system environment So we have different values stored and different values triggering output to screen Data Input Event Driven Applications The user can add and remove beepers manually while the application is running So he can even give input while the robot is moving This way he can communicate with the robot by inputting raw data as beepers You can set up scenarios where the robots work event driven J ust let the robots loop for ever waiting for events such as adding and removing beepers manually
19. Therefore trying to find the ultimate metaphor is not worth the effort 3 Cookbook Approach 3 1 3 2 3 3 3 4 To get a fast success a lot of books use the cookbook approach The cook book approach uses different elements to support learning Overview of this Approach In a book following this approach the text explains usually with one ex ample how to do complete programming tasks The book gives a code model how to complete the task efficiently Therefore there are two ele ments example code and how to do prescriptions The J ava Tutorial Campione 1997 or the very popular German written GoTo J ava 2 Kruger 2000 are examples for such an approach Also there often is complete background information about the most important aspects of the implementation Example Code The most important part of this approach for learning is the example code given The reader or trainee can either reconstruct this example or based on the model construct his variation to the model given in the book personally copy the chunk of code into my project and replace the names of the identifiers How to Do Prescriptions and Background Information Often things cannot be done with just one or two chunk of code This multiple steps the student need to complete often involve several classes Sometimes they involve file handling or even installation procedures Some of this steps are highly interrelated with other questions Ther
20. This adds a little re dundancy This fact adds some extra training at the time when the course leaves the microworld and real J ava coding starts What I miss most in Karel are two things attributes and arguments Both elements are crucial for the collaboration of robots As regard col laboration as the most important aspect in object oriented programming miss this feature badly J Karel The textbook to J Karel is completely based on Karel But J Karel can much more J Karel is written in pure J ava and completely object oriented The robots of J Karel are defined in regular J ava classes that implement the interface Direction J Karel even allows multithreading The disadvantage of J Karel is exactly its strength The user works in a J ava class and sees there some of this confusing code elements that would rather like to hide from him He sees for instance the static method main or the import of the package kareltherobot The class must be 67 4 4 Chapter 5 Existing microworlds for teaching J ava saved as Main java execution starts in the method main of this class The class has to be compiled etc Conclusion All three worlds lack some important features The Hamster Model is not object oriented Karelt has no attributes and no parameter passing J Karel does not hide well enough the ugly object oriented overhead Starting with Karel and switching to J Karel seems to be an option
21. a visual rep resentation called control a text a slide bar into data and data back into representations on screen Not knowing this fact novice programmers expect that they can manipulate directly data from TextAreas Lists or J Tables For instance they expect that they could use directly a TextArea for a calculation or that they work with a J Table without defining a data model for the Table How to scope with this problem The System out printin A pproach Extensive use of sending information to standard output a text window helps users to see what is going on You may later even instruct your people to first set up a data model that you test only by observing the 26 8 5 8 6 Chapter 3 Key problems of teaching object oriented programming line output produced with System out printIn Only when this model works fine you integrate it in a graphical user interface While doing the integration you take care to explain the process from con trol to data and from data to view Making Input and Output Easier with J ava J ava is a GUl oriented language Access to input and output is difficult It is all natural to lower the cognitive load by avoiding the GUl overhead and hiding the complexity of input and output in the beginning Several train ers or authors do this J udy Bishop 1997 uses a class Text to ease ac cess to files and keyboard Not all readers appreciate her way to do it One reader on Amazon c
22. and output streams strongly recommend to start learning the most common design pattern and their visual representation with Unified Modelling Lan guage before learning these parts of the API 2 Learning Design Patterns and Unified Modelling Language with Roboworld 2 1 Motivation As things are obvious and simple the teacher can introduce the diagrams of the Unified Modelling Language UML easily This way one can build in the trainee s mind a visual representation of the patterns used in the solu tions set up in the microworld The trainee will relay on this system later when designing complex and abstract applications or while reading design or analyse patterns It is quite difficult to build such a representation of patterns for classes and objects when there are no simple and under standable examples Examples that are close to programming problems 90 2 2 2 3 Chapter 8 Supporting the Unified Modelling Language Design Patterns You can use and discuss design patterns from the very beginning For in stance for the roofing we may use the pattern template methods would strongly recommend to use UML diagrams and name the design patterns used in the process of problem solving would also suggest to think about scenarios where different types of design patterns could actu ally be used This way the visual representation with UML can be learned step by step Starting with a simple class box to show the r
23. appealing The advantage of the solution of the Hamster Model is its simplicity But it needs no further discussion It has nothing in common with object oriented programming The solution of Karelt gives the trainee the wrong impression that there must be a main task But the modular thinking of object oriented programming should teach that there is no main task Plus it needs fur Fl 4 2 4 3 4 4 4 5 Chapter 6 Reducing cognitive load in Roboworld ther manipulations when the students like to test a single method they have written Solution Part One an Instantiation Tool Fig 17 the instantiation tool The figure above shows the instantiation tool The user may choose from any of the robot types he has defined in a class or he may use the basic API class UrRobot With the four arguments he may specify column row direction and number of beepers that the robot is carrying The graphical display of the instantiation tool follows the syntax of J ava It does not follow the subject predicate logic This is done on purpose Solution Part Two Better Trigger Different Operations Manually than Running J ust One Main Task to Reinforce the Paradigm of Object Oriented Programming According to the paradigm of object oriented programming robots should be built to do several tasks and these tasks are more or less equivalent usually So the user should be able to trigger different tasks manually To build a batch of all p
24. direction number of beepers are visible from the very beginning With al most no prerequisites after some basic instructions how to operate in the microw orld the trainee can see how operation calls change the informa tion in the attributes He also sees that the call to update operation is the only way to change the objects attributes There is now way to change objects attributes directly One important information that might be saved in an attribute is the link to other robots if there are robot teams in action Other than in the existing world Karel Hamster Model attributes link to other robots So one can show the important fact how associations are handled after a short time of instruction Instantiation of Robots You can get a new copy instance of a robot by setting its initial values and call for a new robot This instantiation can be done manually So the trainees sees first what new means and that an instance is nothing else than a new copy of an object He or she sees the serial number and the class of the robot when he or she chooses the robot from the list of ro bots This information is also visible in the sequential output that he or she sees in the pane at the lower right of the window All this helps the stu dent to get a representation of robots and objects as instance of a class Inheritance Overriding Polymorphism Even the first robot inherits from UrRobot the basic attributes and methods With
25. little information key word super the trainee can alter override the inherited methods for instance to define a robot Dou bleStepper or MileWalker that makes two or more steps when it gets 86 Chapter 7 Explaining basic concepts with Roboworld the instruction to move The microworld shows in the feedback area to the lower right of the screen from what class of robot the applied method is taken Inheritance this way becomes an all familiar idea 2 6 Conclusion Robots are the most accurate visible representation of objects in object oriented programming They are the most powerful metaphor for them that we can think of 3 Application Programming Interface API It is always difficult to get an idea what an application programming inter face API is for In a microworld this is easy to see If there would not be the class UrRobot the basic methods for manipulating the robots would be missing We need this basic operations to do anything in the world This is the smallest and the most figurative example of an application pro gramming interface that can think of 4 Conclusion A microworld of robots is a most accurate representation not only of ob jects in object oriented programming but also of other basic concepts such as data storage data input and output sequentially and randomly acces sible data or the application programming interface As accurate meta phors support learning Iding 1997 this
26. main problem is that trainees stay inactive Therefore there is little likelihood that they acquire new schemata Why and When Metaphors Do Not Work J ean Piaget first recognized the power of metaphors He made a link be tween the struggle for survival in biology and the struggle for survival in learning situations Firstly beings are trying to implement their existing strategies for survival in new situations They pick the strategy for the most likely situation they know This is known as assimilation So the main reason to pick a metaphor is to make the trainee do most likely the right thing or something that is not completely erroneous If he does something wrong the trainee must get a feedback that makes him adopt the right behaviour This is called adaptation Therefore metaphors w ith out activity are little help Metaphors will only do their job if the trainee is active and gets enough feedback so that adaptation takes place There Is No Evident Metaphor The high variety of metaphors used in object oriented programming shows that there is no evident metaphor to explain objects and inheritance Some of the metaphors used are listed below e In the J ava tutorial 1996 through online 2001 in chapter Object Oriented Programming Concepts A Primer the metaphor of bicycles is used e Eckel uses a light bulb Eckel 1997 p 29 to explain an interface 32 2 5 2 6 Chapter 4 Existing solutions to overcome the problem o
27. move Karel putBeeper Karel move Karel turnOff End Task End Program Fig 10 Karel the robot in action 3 The microworld is a closed world not an visible small part of a bigger problem Therefore the trainee does not feel the need to see behind the curtains or around the corner 4 The trainee gets sensible tasks to complete With a given small amount of new knowledge he is able to complete the task He can even invent his own problems and solve them 5 The trainee gets immediate feedback He sees where his code runs successfully and where it fails 52 9 3 Chapter 4 Existing solutions to overcome the problem of cognitive load 6 The API of the microworld is very small In the Hamster Model the trainee works in a predefined class Hamster in Karel the trainee subclasses one of two basic classes or one of his own classes See the follow ing figure ur_Robot row int colom int Hamster beepers int direktion north east south w est update constructor vor move ur_Robot street int avenue int direction beepers int linksUm turnLeft update nimm pick turnLeft gib put move query pickBeeper vornFrei boolean frontlsClear placeBeeper maulLeer boolean mouthEmpty destructor kornDa boolean isSeedThere turnOff Robot c
28. ohn 1994 Design Patterns Elements of Object Oriented Software Addison Wesley Goguen J A 1996 Semiotic Morphisms http w ww cs ucsd edu users goguen papers sm smm html Gibbons J 1998 Procedural Programming in J ava SIGPLAN Notices V 33 N 4 April Goll J Weiss C Rothlander P 1999 J ava als erste Programmiersprache B G Teubner Stuttgart Hunt J McManus A 1998 Key J ava Advanced Tips and Techniques Springer London Iding M K 1997 How Analogies Foster Learning from Science Texts Instructional Science 25 233 253 Jones A 1984 How Novices Learn to Program Proceedings of the First IFIP Conference on Human Computer Interaction INTERACT 84 London King K N 2000 J ava Programming From the Beginning Software online at http knking com books java index html Kruger G 2000 Go To J ava 2 Addison Wesley free online at http www javabuch de Langer Schulz von Thun F 1974 Messung komplexer Merkmale in Psychologie und P dagogik Ernst Reinhard Verlag M nchen Langer Schulz von Thun F Tausch R 1981 Sich verst ndlich ausdr cken Ernst Reinhard Verlag M nchen Lewis M D 1980 Improving SOLO s User Interface An Empirical Study of User Behaviour and a Proposal for Cost Effective Enhancement Technical Report No 7 Computer Assisted Learning Research Group The Open University Milton Keynes England Mendelsohn P Green T R G amp Brn
29. one object So the experience we made with Unified Modelling Language also sup ports cognitive load theory 46 5 11 Chapter 4 Existing solutions to overcome the problem of cognitive load We introduced also use case and activity diagrams The experience with these two types of diagrams were poor They are not so closely related to the paradigm of object oriented design would avoid presenting this ma terial in the same course cycle in the future would use user stories in stead of use cases because students always tried to define several use cases even for very small projects Conclusion Based on reported and own experience can say that CRC Cards support the learning of basic concepts of object oriented programming This gives support to cognitive load theory mainly because of CRC Cards goal free usage Some diagrams of the Unified Modelling Language can help to learn schemata of object oriented programming This is especially true for state chart diagrams Other static and dynamic diagrams show more interrelated elements Introducing three kind of dynamic diagrams statechart dia grams sequence diagrams and collaboration diagrams was redundant and might be a reason for the poor performance with this kind of diagram Also these experiences give support for cognitive load theory 6 Giving a Single Simple Task within an Existing Object Oriented Framework There are three main approaches on this promising track One i
30. ples for math you have the goal and the given There is a multiple step procedure from the given to the goal The goal the given and the possi bilities in between overflow the learners working memory If the learner has only the given and the task to find out what ever he can he performs and learns much better The worked example effect implies to give students worked examples to study This way they can build schemata The teacher uses problem solv ing only to test if training has been effective The split attention effect suggest to avoid that the student has to look up information at different places Examples for splitting attention are for in stance Working with a textbook and at the computer screen at the same time or explaining the semantic elements of a diagram in the text outside the diagram instead of explaining these elements directly with notes on the diagram Footnotes and endnotes The redundancy effect suggest to avoid to show similar content twice Examples of redundancy are for instance Adding pictures that do not ex plain the material that should be learned to a text book Sauders amp Sol man 1984 Upgrading a text with vivid but lengthy examples See Langer e a 1981 p 139 who did extensive research on readability in German The modality effect says that some portions of working memory are sen sory mode specific That means you may expand working memory when using different modes of presenting informati
31. software that complies with them Chapter 1 Cognitive load in a J ava short course Most interesting in the view of cognitive load is the first cycle of our J ava short course because it is the most demanding A lay out of the knowl edge needed is shown in fig 1 as use case diagram To be able to write an uncomplicated J ava application the trainee needs all knowledge related to the three icons that show person figures labelled with basic object oriented intermediate object oriented and J ava programmer A lot of interrelated information is needed even to write a simple J ava application without graphical user interface There are seven topics interrelated with this first milestone Usually this topics are teached as follows Instruction how to set up the J ava Developer Kit how to enter the text of the application Hello World how to save compile and run this simple application This is the prerequisite to start learning Therefore this prepa rations are not in the diagram Secondly the student learns how to store values in variables of primitive type and how to perform basic operations Sometimes this is done simul taneously Thirdly the student learns the use of control structures Usually This is not possible without variables and Boolean operations Hence to study control structures includes variables and basic operations Then comes the hard core of object oriented programming where it is difficul
32. the other The main task method is the same for all robot classes In the house painting example a basic roofer class that paints a standard roof may be sub classed by roofers that paint a flat roof or a steep roof Robot Teams Collaboration Strategy In the harvest example we can have a team of robots harvesting the field the more rows a field has the more robots we need to do the job In the house painting example Instead of having one robot that makes walls doors windows and roofs we use a team of different robots to do the job This example is very figurative because as Bergin shows we can have a carpenter a roofer a mason and a contractor who coordinates the team 64 Chapter 5 Existing microworlds for teaching J ava 2 6 Link to Object Oriented Design Robot names and method names are crucial for writing readable code The trainee sees the advantage of using talking names for classes and meth ods For instance a RooferForFlatRoofs gets the instruction to make3UnitsRoof Variations in behaviour of single robots are usually done by sub typing polymorphism not by providing more methods for one single type of robot By setting up different robot teams for different houses one can see the power of aggregation With robot teams aggrega tion one can combine different types of roofs windows walls and doors to construct a vide variation of houses 2 7 Advantage of Microworlds In the microworld you get al
33. to perform operations on itself by making requests But this book is not regarded as a book for beginners This is at least what the feedbacks of beginners at amazon com Say Basic Programming Knowledge before Getting to the Paradigm of Object Oriented Programming As already mentioned some books and teachers give first an introduction to parts of J ava that are not related to object oriented programming data types expressions statements control statements etc This is an in termediate approach between giving a sound theoretical background firstly and teaching procedural programming firstly The cognitive load is lowered a bit this way but the problem how to introduce the paradigms of object oriented programming still remains unsolved So this approach is only a variation to giving a sound theoretical background first Among the books that follow this track are J udy Bishop s J ava Gently Bishop 1997 Her bert Schildt s J ava 2 A Beginners Guide Schildt 2000 or in German Guido Kruger s GoTo J ava 2 Kruger 2000 Conclusion Despite all the good ideas and efforts to find convincing metaphors there is little success in this approach The level of learner s activities is too low and the space of time to writing code is too far so that either learning of schemata does not take place or that the transfer to implementing code 34 Chapter 4 Existing solutions to overcome the problem of cognitive load gets hindered
34. to produce such works If chunks of code are not to large this Read before Write element can be recognized as the worked example effect mentioned in cognitive load the ory Bergin suggests rather using large case studies than a textbook with a cookbook approach It seems to me to be an important question how the worked example effect is best integrated in programming Giving large project to read which show the important chunks of code in context or using very small examples that give a minimum context to understand the single chunk of code that the student should study In any case this Read before Write or worked example effect is a big advantage of this approach Software Leaming and Chunk of Code Learning how to program is highly related to learning code elements that are used repeatedly Some examples of important chunks in J ava Usage of the chunk how the chunk looks Starting point of an public class NameOfClass application public static void main String args lt application starts here gt Query method typeA variableNameB typeA getVariableNameB return variableNameB Update method typeA variableNameB void setVariableNameB typeA variableNameC variableNameB variableNameC Looping for a fixed for int i 0 i lt times i number of times lt repeated task gt Table 2 typical chunks of code in J ava This chunks represent a medium level schem
35. writing objects Table 3 Topics mapped to chapters in a book that uses the spiral approach J oseph Bergin 2001 emphasises the problem solving aspect of the spiral approach Students should be able to address real world problems with the knowledge they learnt in every iteration King 2000 tries to help his readers students to do so with Teaching problem solving skills some program design code writing style and give real world examples that are interesting enough and not to large Some of his case studies are Unit conversion course average checking an ISBN number decoding social security number a phone directory printing a one month calendar playing blackjack 4 3 Cognitive Load of this Approach This approach reduces dramatically the cognitive load A lot of care is taken to avoid redundant information King defines in his book exercises that enforce the students to learn the schemata they need later in the book 40 4 4 Chapter 4 Existing solutions to overcome the problem of cognitive load Conclusion The example shows that a Spiral approach is possible also without mi croworlds But the price is high King needs 370 careful written pages before he gets to the main topics of object oriented programming writing classes and subclasses SAMS famous J ava in 21 days covers the same topic in the first week Nevertheless would highly prefer Kings careful approach to the way other books about J ava treat th
36. 10 dir 0 carries 10 areThereBeepers as UrRobot true lt Sender 14 c 10 r 10 dir O carries 10 areThereBeepers as UrRobot Loop 1 enter true gt Sender 14 c 10 r 10 dir 0 carries 10 getBeeper as UrRobot done lt Sender 14 c 10 r 10 dir 0 carries 11 getBeeper as UrRobot gt Listener 15 c 3 r 4 dir 0 carries 0 beeperGetted as Listener gt Listener 15 c 3 r 4 dir O carries 0 turnLeft as UrRobot done lt Listener 15 c 3 r 4 dir 1 carries 0 turnLeft as UrRobot done lt Listener 15 c 3 r 4 dir 1 carries 0 beeperGetted as Listener gt Listener 16 c 7 r 4 dir 0 carries 0 beeperGetted as Listener gt Listener 16 c 7 r 4 dir 0 carries 0 turnLeft as UrRobot done lt Listener 16 c 7 r 4 dir 1 carries 0 turnLeft as UrRobot done lt Listener 16 c 7 r 4 dir 1 carries 0 beeperGetted as Listener gt Sender 14 c 10 r 10 dir 0 carries 11 areThereBeepers as UrRobot false lt Sender 14 c 10 r 10 dir 0 carries 11 areThereBeepers as UrRobot Fig 26 listing of the sequential execution of collaborating robots This output is a good starting point Students can translate this sequence of calls to robots into a sequence diagram All what the students have to do is to design in top the three objects and start ing from top to bot tom the messages sent between the robots See F below 14 Sender 15 Listener
37. 2 3 2 4 2 5 Chapter 7 Explaining basic concepts with Roboworld The Idea of Robots May Help Understand Objects Even Better In real J ava applications you can think of robot teams working on data views and controls The robot s name identifier implies for which object or tasks the robot takes responsibility When we say that a object is doing something then we can think of a robot to be in action that is responsible for this object For instance a robot of class TextField is responsible for the TextField When he gets the instruction setText Hello World he changes the text displayed in the TextField for which he is responsible The idea of robots being in action instead of objects being in action might overcome the natural blockade of students when they have to do with unanimated objects mean objects that students do not associate at all with any activity remember in a course where we were modelling a washing machine that students did not like to award any responsibility to the laundry Objects are a data model of the reality that we are modelling As a result we can imagine that there is for any object a robot in action This robot manages the data of its object Later we may merge the idea of the robot and its object to one idea the idea of the object in object oriented programming Attributes Association Aggregation Collaboration Information is stored in robot s attributes These attributes row column
38. 38 39 40 41 65 74 Kruger 35 Langer 4 6 61 96 97 Learn mode 73 Lewis 14 Long term effect 63 Long term memory 3 Main task 72 Manually instantiate robots 71 Manually trigger operations 72 Mathematics 33 50 63 89 Mendelsohn 63 Messages between robots 76 Metaphor for objects 85 Metaphors 32 and microworlds 34 Effectiveness of 33 Metaphors for Pointers 17 Metzger 60 Microworlds for training 51 Mind maps 58 Modality effect 4 57 70 Modularisation 13 Multiple choice questions 58 Name space as novices problem 15 Niemann 33 Novices problems with procedural programming 14 Object diagrams 43 Object Management Group 22 Object oriented design 65 object references 16 Object references 82 Objectives in a J ava short course 3 Object oriented programming problem solving strategies 11 teaching 1 Object oriented programming motivation for 10 Novices problems 14 Objects explained directly 34 Offline teaching 57 Operators 81 105 Overall control 83 Overriding methods 79 87 PairProgramming 56 Papert 63 72 83 Paradigm of object oriented programming 19 Parser 70 Pointers 16 82 Polymorphism 24 83 87 Problem domain 55 Problem solving and microworlds 62 65 Problem solving strategies 10 Program flow 44 Programming environment and cognitive load 9 Programming in Pairs 56 Rajan 14 63 Rating 61 Read before Write 27 36 48 Readability of German text 6 Reading comprehension of diagrams 44 Recurs
39. 89 mention that in the model view control pattern the model has no collaboration with the model or the con trol Collaborations with them are not a must only a possibility The model may be driven without a graphical user interface Afterwards CRC cards can be used in three ways 1 You can derive static class diagrams from these cards 2 And most important you may set up a team in which everyone plays an object of one of these classes Then you try to accomplish a task From this role play you can derive dynamic diagrams as statechart or most likely collaboration diagrams or sequence diagrams 3 Experienced programmers can transform CRC Cards directly into code It is in the second way where CRC Cards may be used in education Statechart Diagrams Learners are confused by a high number of objects working together A statechart diagram studies only one object in different states of its lifecy cle Learners understand simple statechart diagrams long before they completely grasp the sense of attributes and operations Work ing with statechart diagrams is therefore a powerful tool to Full guide learners from their real live filingStopped understanding of the behaviour blose tank of objects to the functioning of objects in object oriented programming A fuel tank is a good example for an object with states that stu dents understand easily The tank may be full empty filling and ready It has two attributes Capacity an
40. Universit de Gen ve Facult de Psychologie et des Sciences de l Education TECFA Technologies et Formation de I Apprentissage Roboworld Overcoming the Problem of Cognitive Load in Object Oriented Programming by Microworlds M moire en vue de l obtention du DESS en Sciences et Technologies de Apprentissage et de la Formation Hanspeter Heeb http tecfa unige ch heeb hanspeter heeb tgnet ch Defended on October 31 2001 Jury Dr Daniel SCHNEIDER Charg de cours TECFA Universit de Gen ve thesis director Dr Daniel PERAYA Maitre d enseignement et de recherche TECFA Universit de Gen ve Paraskevi SYNTETA Assistante d enseignement TECFA Universit de Gen ve Acknowledgement Thanks to Daniel Peraya He granted me a second chance after my first Master thesis about touch typing failed because of missing user data Thanks to Daniel Schneider that he was flexible enough to scan the draft of my Master thesis and giving me valuable feedback Thanks to J oseph Bergin who first adapted the idea of learning program ming with microworlds to C and J ava Also he is one of only few teachers in the field who publishes his findings in the web Special thanks to all those students in my short course Their feedback was one of the major sources to write this thesis and the best motivation to set up a microworld that should make learning J ava more fun Thanks to the persons who have been helping me to pro
41. a application write and call operations lt Return Type includes Arguments 2 call static operations from own classes perform basic operations use simple predefined operations extendes extendes basics structural rite operation ite and call with simple instanciate and call fe Sahay arguments gt Operations from API classes instanciate and call operations fromown classes Shneiderman to code use recursive procedure call corretly encapsulate attributes translate dynamic diagramms to code use pointers and references write Nassi Shneiderman diagrams write simple define classes for value objects write simple static diagramms y define records intermediate str define abstrac classes and use in out and io interfaces arguments modullarise programms define classes for referenced objects write a java gui application ake a double clickabl windows java archive use java input output api use wrapper classes for collections includes avoid side effects read javadoc documentation work with threads generate documentation w ith javadoc java programmer Fig 1 curriculum and its dependencies as use case diagram 4 2 4 3 Chapter 1 Cognitive load in a J ava s
42. a hamster instead of a robot and nuts instead of beepers but the possible trainings remain the same This Hamster Model explains only procedural programming An extension is planned that teaches object oriented pro gramming But this extension will not be finished before 2003 51 9 2 Chapter 4 Existing solutions to overcome the problem of cognitive load There are Several Obvious Advantages of Microworlds Like Karel or the Hamster Model 1 The trainee can solve a given problem with a small amount of knowl edge For the first problems the trainee has only to know two commands pickUp and move 2 There is not a big overhead of file handling programming environment or DOS Unix command line instructions In Karelt the user sets up a world or opens a saved world with a given problem He edits the program code and starts the program The program may be executed step by step or non stop Two windows are giving feedback about the robots their state and about errors or completion The user can combine several classes by the C keyword include Basic example of Karel code left and microworld with problem to solve Class and Method Declarations Begin Task k FIRST WLD _ O x 001 002 003 004 oos oo mil task Declarations ur_Robot Karel 1 2 East 0 Statements Karel move Karel move Karel pickBeeper Karel move Karel turnLeft Karel move Karel
43. a large framework It asks for different key skills as doing fixes in an exist ing project It ask for skills such as understanding specifications and meet them writing code from scratch instead of scanning for a problem and fix it 50 Chapter 4 Existing solutions to overcome the problem of cognitive load 9 Using Microworlds for Training 9 1 Microworlds have been widely used for teaching programming procedural programming Dietrich Boles 1999 adapted this earlier work for proce dural programming with J ava J oseph Bergin 1997 to C and to ob ject oriented programming with J ava Bergin unpublished Short Overview of the Three Existing Worlds Karel the robot uses a microworld with robots that do tasks with beepers They can walk turn left pick up beepers and lay down beepers Walls make tasks more complicated As its name implies Karel uses a simple code with similarities to C J Karel is an adaptation of Karel to J ava It uses pure J ava code This means the robots are coded as regular J ava classes The world looks the same as in Karel and the textbook is based on the textbook for Ka relt It has not been published officially yet Trainees can use all the power of J ava when sub classing the Basic Robot classes They may ex periment even with multithreading and solve problems with several robots running in several threads Written in German there exists a J ava programmed world that uses
44. a which is stored in the pro grammers long term memory Such chunks are at about the same level as often used sentences in natural languages Major Disadvantage of this Approach In a rapidly moving course there is a great risk that trainees jump from topic to topic without understanding any fundamental concept They even not stock any chunk of code The teacher may have the feeling that train ees are doing well because they succeed in generating nicely looking ap plications by copying large part of code and imitating code models with 36 Chapter 4 Existing solutions to overcome the problem of cognitive load some support of front runners and the teacher remember a course where did some repetition on remote method invocation RMI The main problem was that students did not understand method invocation with the passing of parameters and return values Sixteen trained students had no idea how to pass more than one value of a primitive type back as re turn value They did not know what query and update methods were and how they really worked 3 7 Psychological Reason for the Weakness of this Approach In the view of cognitive load often the attention is not splitted Crucial code elements are commented directly in the code example So one would expect that this approach should do fine But there is very often a large amount of unnecessary information Usually the code examples demand a basic understanding of a lot of concep
45. a P 1990 Programming Languages in Education The Search for an Easy Start In T Green T Hoc J M Samurcay R Gilmore D Psychology of programming 175 194 New York Academic Press Traduction francaise en ligne Metzger Ch Waibel R Henning C Hodel M Luzi R 1993 Anspruchsniveau von Lernzielen und Prufungen im kognitiven Bereich Studien und Berichte des IWP Heft 10 Institut fur Wirtschaftspadagogik an der Hochschule St Gallen 108 Bibliography Niemann A 2001 Objektorientierte Programmierung in J ava 2 A verlag moderne industrie Buch Kaarst Object Management Group Inc 2000 Unified Modeling Language Speci fication vers 1 3 March published online Papert S 1980 Mindstorm Children Computers and Powerful Ideas New York Basic Books Rajan T 1990 Principles for the Design of Dynamic Tracing Environ ments for Novice Programmers Instructional Science 19 4 5 377 406 Schr ter Brit Plank J ohann 2001 Selfjava version 1 08 http w ww selfjava de Schildt Herbert 2001 J ava 2 A Beginner s Guide Osborn Mc Graw Hill New York Sweller J 1988 Cognitive load during problem solving Effects on learning Cognitive Science 12 257 285 Sweller J Chandler P Tierner P amp Cooper M 1990 Cognitive load in the structuring of technical material J ournal of Experimental Psychol ogy General 119 176 192 Wilson Brent G 1995 Maintaining the T
46. a relationship between the kind and number of objects at each end of an association and the type of collection best suited to maintain this relation ship The trainee must learn this relationship between association drawn in a chart and the collection used to maintain references CRC Cards and Role Play Working with CRC Cards to test program flow is an excellent way to ex perience the way collaboration in object oriented programming works J o seph Bergin calls this Design by walking around would call it an objec 23 6 4 6 5 Chapter 3 Key problems of teaching object oriented programming todrama because do not only use CRC Cards for designing new interac tion but also to replay existing interactions For instance replay with my students the event processing of the graphical user interface How to Use CRC Cards and Role Play Students tend to use interaction sequences were one object takes control and the other objects stay more or less passive That means they do more or less procedural programming One object takes the part of the struc tured program the other play the role of records that store information You end up with programs where one class is extremely long all other classes are short and have only simple update and query methods Even trainees that never learned procedural programming show this tendency To prevent this structured thinking you may give your students different restrictions for the way th
47. aching Teaching control structures is not a big problem in object oriented pro gramming It can be taught also by traditional exercises easily It is still good to know that Bergin 1997 p 96 to 146 and Boles 105 to 150 show a lot of examples that are fun 3 1 The If Statement Gives Robots a More Flexible Behaviour The if statement makes the harvest easier If there is a beeper harvest it This way robots can harvest fields where some beepers are missing 65 3 2 3 3 Chapter 5 Existing microworlds for teaching J ava Bergin 1997 p 80 82 uses hurdles to introduce the If Else statement If there is a hurdle jump over it else go ahead Save Operating You can define methods that avoid robots crashing because they run out of beepers to put try to harvest a beeper that is not there or run into a wall or another robot This is a very good example of the if statement because avoiding exceptions by checking whether the necessary condi tions for an operation are met is an important strategy to write nicely run ning applications While Statement Good examples for the usage of while statements are fields of variable size while field has not ended and with an unknown number of beepers on one cell while there are beepers You can set a wall surrounding a range that has no beepers on some cells Fig 14 mountains of variable height or sinks to test while loop Walking over a mountain of undefined heigh
48. alance where the value of balance a local value is assigned to the field called balance If there is no field balance there could even be a class variable balance These fields and class variables might be defined in any basic class of the current class Even if you have not understood this explanation because you are unfamil iar with object oriented programming you have seen that the cognitive load is heavily increased compared to procedural programming Sometimes learners are so confused that they even doubt whether value passing goes from left to right or from right to left Usual Attempt to Solve this Problem Make learners to send the content of variables to the standard output System out printIn throughout the program flow Instruct them to use different names at different places for variables that handle the same information data in different classes and their opera tions This way they learn at least that value passing is independent from variable names Conclusion It is preferable that the schema of objects and classes and the collabora tion of objects are generated in trainees mind before variables as a major topic are introduced Otherwise the cognitive load is overwhelming A microw orld should support the acquisition of the most important type of variables objects variables 2 Understanding Pointers or Object References 2 1 The concept of object references pointers is known as complex In ob jec
49. an attribute within a query method In a usual project you would program a method rightIsClear directly by querying the position and direction of the Robot and checking whether there is a wall or the borderline of the microworld to the relative right of the robot Side effects are not covered in a good curriculum for object oriented programming But implicitly you teach Never ever use an up date method for a query method as the golden rule for avoiding side ef fects Solutions to this Design Flaw Boles 1999 uses this effect to explain the concept of side effects which is important in procedural programming As Boles explains in Chapter 2 procedural programming before introducing object oriented programming in the following chapters which will not be available before year 2003 this work around is adequate Side effects are an important topic in procedural programming In procedural programming this problem cannot be ad dressed by the simple technique of not using update methods for a query Bergin 1997 uses this unintended effect to explain the fact that the re turn statement terminates immediately execution And therefore you Cannot put the last turnLeft operation after the return statement As side effects do not occur in object oriented programming usually Bergin 1997 does not discuss side effects Microw ords in the View of Cognitive Load Theory By reducing the problem domain to a microworld the intrins
50. an object before they constructed an in stance of it As the compiler s error message says something about static they try using static attributes Also as you worked before in the static main method you might have introduced attributes there Therefore if you introduce attributes before you introduce instantiation you will run into big problems Your students will remember static attributes as some thing you use regularly They do not see it as something very special you use only for specific tasks 5 2 A Good Remedy Treating Static Elements as a Special Object Besides teaching the process of instantiating well so students don t run into compiler errors or teaching them how to fix this problem properly found the following explanation of static attributes and operations accu rate visualise static attributes in an object diagram For instance in the ac count example show classes and the content of their attributes as ob jects Account CurrentAccount SavingsAccount PrivateAccount nextNr 501 LOAN LIMT 10 000 LOAN LIMT 0 LOAN _LIMT 5 000 TYPE 17 TYPE 15 TYPE 14 11 CurrentAccount 120 SavingsAccount 52 SavingsAccount 7 PrivateAccount number 17 000 204 number 15 000 420 number 15 000 123 number 14 000 010 amount 5 203 50 amount 25 780 90 amount 920 10 amount 4 20 10 Custo
51. andard output Table 1 Programming Environment Also the programming environment adds to the cognitive load There is no programming without a programming environment The set up of the programming environment has become easier with J ava 1 2 Still a lot of know ledge is needed For instance to use predefined classes Such classes Chapter 1 Cognitive load in a J ava short course are provided as part of some courses or are crucial for some exercises Complexity bursts when packages are used or introduced The trainer has to decide whether to use a software developer tool like J Builder that helps in generating and managing projects or to use a simple editor like EditPlus Choosing the first option means teaching the overhead of a sophisticated software Choosing the second option re quires a sound understanding of the file system text editing and the us age of a command line operating system like DOS or Unix 4 4 Technical Terms The amount of technical terms especially the terms in the feedback pro vided by the compiler is high For trainees who are unfamiliar with English the English language adds to the cognitive load as well 4 5 Graphical User Interface Programming graphical user interfaces GUI is rather complicated Setting up a user interface with swing is very well documented in the J ava tutorial Nevertheless because of its richness and complexity it is impos sible to understand f
52. ars and haven t made the move to object oriented programming completely One of my colleagues at our institution for adult education made for a 30 1 3 1 4 1 5 Chapter 4 Existing solutions to overcome the problem of cognitive load case study in object oriented programming a model solution Analysing the code you can tell that this colleague hasn t made the transition from pro cedural programming to object oriented programming either guess the shortage of material and teachers will continue for some years procedural programming projects with J ava It is possible to create all in one class procedural solutions for smaller pro jects For instance with an applet the student can create interesting ap plications He takes the inherited methods as if they were predefined pro cedures in a procedural language Draw backs of this approach There is some drawback to this approach Object oriented programming is still quite different from procedural programming When setting up a time budget for your course you might carefully plan where you can spare time for teaching the most important concepts of object oriented programming You may check existing course books for topics related to procedural pro gramming like decision tables Nassi Schneiderman diagrams recursion side effects and modules Experience shows that learners show a big affinity for a structural ap proach to solve some programming problems With this ap
53. ask rating robots Inheritance key word BigHorse 5 move Super Sender Listener 2 Sender 14 1 newListeners Listeners 2 waitForUser 3 see page 4 You may also open a new empty scenario 99 1 2 Appendix A User Manual When closing the window by clicking the close box you get back from the scenario window to this window with the list of scenarios You may save changes to a scenario open a new scenario open a saved scenario dispose a scenario exit the application Inside a Scenario Add and re move walle Compile an instanti World with i able class numbers i e ees data Beeper and Objects Robots and Walls LiRaboter charis void doTaski i Instantiate T Feedback about code execu tion active robot learning macro mode the operation is entered in the operation Standard procedure 1 Choose new Class in the list of class above the editing pane 2 In the pane for code editing you define methods by entering existing operations like move or turnLeft See the doTask template in the scenario Demo of two collaborating robots 100 Appendix A User Manual 3 Click Button Compile to make the class available for instantiation and check for elementary mistakes 4 Click on new to instantiate a robot of the type of class left to the but ton new Step for can also be executed as step 1 for existing robot classes like UrR
54. at the book was too basic or al most too gentle as positive not as negative feedback Microworlds are used at colleges and universities with success Design Flaws of the Microworlds There lies a minor inherent design flaw in these microworlds Usually in object oriented programming you have either update or query methods What is the difference between update and query Objects contain in formation For instance the position of a robot in Karel and its direc tion are information contained in the robot Position and direction are called attributes or fields of the robot Either you update this information by methods like move or turnLeft or you query this information by methods like isFacingNorth Query methods return a value in Karel the Boolean values true and false In object oriented programming usually you do not use update methods if you define new query methods Bergin 1997 page 73 explains how to define new predicates query methods For defining an operation rightls Clear he uses the update method turnLeft in this method Therefore after three turns to the left and checking frontlsClear rightls Clear the robot is facing to the right So he has to turn it again to the 54 9 7 9 8 9 9 Chapter 4 Existing solutions to overcome the problem of cognitive load left to avoid a side effect A side effect is an unintended update of infor mation contained in an object
55. ated to other topics they should be available in microworlds To reduce cognitive load use only attributes At the moment it is only possible to reference robots But the idea is that it should become possi ble to pass robot references by messages and store them in attributes This way a lot of design concepts and execution schemata could be learned in the microworld By displaying the message with the value sent from robot to robot the trainee does not need to imagine this value as it is the case outside the microworld Object references are visualised as serial numbers of the object Therefore it is easy to see for the trainee that the receiver of the message now knows the reference number sent to it He only needs to assign it to an attribute The example with the sender and the two receivers might give a first glance on the powerful tool Roboworld will become when it not only can assign robot references to an attribute to refer to other robots but also can pass object references from one robot to the other 6 3 Conclusion Working with instance variables attributes and only them causes a mini mum of cognitive load and enables a maximum of schema to be learnt 7 Defining Classes To lower cognitive load there is a template class to define new types of robots objects The trainee can use this template use the learn macro feature to add operation calls So with almost no training he writes his own Classes that do inte
56. be ginning plan to watch trainees closely during classroom training and check for the most common failures These failures plan to catch at compile time and give trainees the most accurate remedial information In a later version all remedial information should be kept in a text file that the program imports at start up This way the remedial information can be translated into different languages Probably the best solution would be to have the remedial information spo ken to the student So he or she could listen to the information while fix ing the code This way we could profit form the modality effect 3 A Panel to set up a Scenario World With Beepers and Walls As in the existing worlds the scenario with beepers nuts and walls is set up by clicking Other than the Hamster Model the scenario shows rows and columns Other than in Karel rows and columns are not referred to by streets and avenues It uses the spreadsheet metaphor 3 1 The Spreadsheet Metaphor The reason for the usage of the spreadsheet metaphor is that people out side The United States are not used to streets and avenues that build blocks Therefore this metaphor might add cognitive load for trainees out 70 Chapter 6 Reducing cognitive load in Roboworld side The United States Spreadsheets are widely used and people are fa miliar with them Spreadsheets refer to columns by letter The number of columns a robot walks is difficult to count with l
57. be fixed or reconsidered Thus would say cognitive load theory might be used to quality check instructional material under con struction Also could think about bringing information together eliminat ing redundancy or arranging goal free situations To conclude would state that cognitive load theory can really as rote rule to apply to instructional material and teaching See Reducing cognitive load in Roboworld starting at page 6 do Cognitive Load Theory and Other Learning Theories In a racing car there is an engine that pushes the car forward But there are weight and aerodynamics that have to be considered too because they might slow down the car In analogy to such a racing car we may see behaviourism cognitivism and constructivism as the engine and cogni tive load theory as weight and aerodynamics A typical example is the famous constructed response frame sequences Behaviourists loved to use it for their drill and practice Because of their redundancy these sequences are inefficient But they can easily be re placed by flashcards These flashcards cards with question in front and answer in the back use the same silly drill and practice as the con structed response frame sequence Only they have less cognitive load Another example Interesting material for explorative learning can be checked whether it is not too heavy for the students A goal free task might reduce in such an explorative learning en
58. bject oriented programming In a J ava short course there is not enough time usually Therefore this approach is problematic 31 Chapter 4 Existing solutions to overcome the problem of cognitive load 2 Giving a Sound Theoretical Background Firstly 2 1 2 2 2 3 2 4 Description Giving a sound theoretical background first is done in lots of books and courses Either After teaching some basic programming in J ava or in the very beginning In any case it should be done before instantiating objects and defining entire classes To explain objects technically to novices is almost impossible Therefore most authors rely on to metaphors to explain objects classes inheritance polymorphism or objects in action There fore discuss at this place metaphors comprehensively J udgment of this Approach According to the theory of cognitive load this should be a good approach The learner is not forced to split attention and there is no redundant in formation But practical experiences are somewhat disappointing Even if the teacher uses good metaphors he may not gain more then having taught some basic words Whether he uses metaphors or rather stick to more technical explanations there is little hope for successful transfer of the knowledge to a situation where the trainee actually has to write code This means code that uses techniques of object oriented programming like instantiat ing objects and exchanging messages The
59. ble this adds to the cognitive load This is especially true when classes and scenarios are saved separately 69 Chapter 6 Reducing cognitive load in Roboworld 1 2 Overcoming the Disadvantage of this Approach The disadvantage of my solution is loosing flexibility You cannot import a single scenario plan to add this flexibility later by providing import and export functions for single classes and scenarios Yet for a beginner s course this feature is not of high priority 1 3 Expectation Conclusion A list of scenarios should not make a big difference But as the working memory is very limited we should profit also from slight advantages With only about 7 items remembered at the same time in working memory any little improvement counts 2 A Simple Parser Compiler Karel uses its own code and compiler like this feature because this lets you work with a simpler code Also using the J ava compiler may add problems For instance the Hamster World is not compileable offline on a Macintosh computer 2 1 Giving Remedial Information The parser compiler can give other information than the J ava compiler Information can address beginners problems It may allow to forgive more mistakes or to use simpler keywords such as loop instead of for For trainees from foreign languages the teacher might translate error mas Sages and warnings Good remedial information cannot be completely implemented in the
60. c kind of data in the microworld Beepers are of type positive integer w ithout zero This data type is the traditional data type and was in Europe the only data type used until the 15 century There fore for instance accounting uses only this data type In mathematics usually students study this type at first There numbers of this type are called the natural numbers We can conclude that this data type is the most evident and familiar data type We can also represent binary data with beepers If we use only one beeper for each field in an area we can represent binary data 1 2 Data Storage Beepers can be handled Beepers are the basic data taken from external storage and put into internal storage of the robot With walls we may set limitations in size for external data storage The visual representation with blocks of row and arrows represents the nature of computer data in gen eral External data storage consists of multiple series of sequential data We can even make a representation of only sequentially accessible data by limiting access to data using walls Fa RE Se SI Nt a ea a Fig 24 sequentially accessible data 1 3 Data Output J oseph Bergin 1997 p 58 used the robots to do paintings with beepers think this is a excellent idea because it represents data output To en hance the possibilities to visualise aspects of data output added the fea ture of setting colours with beepers use two colour schemes
61. caught handeled within this method param pmt the prompt to be presented to the user return the input as a Number public static double readNumber String pmt String s readLine pmt double out try the entry of the user might not be a number in this case a exception is thrown out Double valueo0f s doubleValue return out catch Exception e the exception is caught here and written to screen System out print1n e the return value is Not a Number because 0 would not be accurate return Double NaN 103 Index Abstract Window Toolkit 28 Access modifiers 81 Account example 24 Aggregation 23 86 inJava 28 Analyse patterns 45 Application Programming Interface 53 87 88 Argument passing 83 Argument passing with messages 18 Arrays 81 Association 86 91 Attributes 78 86 and arguments 68 Beck 41 42 90 Bergin ii 23 27 31 33 34 36 38 40 41 46 47 48 49 50 51 53 54 55 62 63 64 65 66 67 77 84 Bishop 26 33 35 44 Bloom 60 Boles 30 31 51 55 62 63 66 67 Boone 108 Bottom up 72 Campione 35 Chunk of code 36 Class diagrams 43 95 Class Responsibility Collaboration Cards See CRC Cards Cognitive load and Technical Terms 9 Cognitive load theory 3 and readability 6 as learning theory 5 tested effects 4 and Instructional Design 5 Collaboration 22 83 86 Collaboration diagram 91 Collaboration in c
62. change of messages and collaboration of objects rather than program ming sequences Therefore from the didactical point of view prefer col laboration diagrams over sequence diagrams Sequence Diagrams Sequence diagrams are widely used For instance Gamma e a 1994 used them Therefore the knowledge of sequence diagrams is important however they seem to be redundant because they show nothing else than the collaboration diagrams do When students have learned to draw collaboration diagrams we may start teaching the sequence diagram too as an alternative to collaboration dia grams 92 Chapter 8 Supporting the Unified Modelling Language To start with sequence diagrams students may print out the output of the interaction and use this batch to draw a sequence diagram Sender 14 c 10 r10 dir 0 carries 10 ready to run waitForUser gt Sender 14 c 10 r 10 dir O carries 10 waitForUser as Sender gt Sender 14 c 10 r 10 dir O carries 10 isFrontClear as UrRobot true lt Sender 14 c 10 r 10 dir 0 carries 10 isFrontClear as UrRobot Loop 1 enter true gt Sender 14 c 10 r 10 dir 0 carries 10 areThereBeepers as UrRobot false lt Sender 14 c 10 r 10 dir O carries 10 areThereBeepers as UrRobot gt Sender 14 c 10 r 10 dir O carries 10 isFrontClear as UrRobot true lt Sender 14 c 10 r 10 dir 0 carries 10 isFrontClear as UrRobot Loop 2 enter true gt Sender 14 c 10 r
63. course designers stated the following key competencies that relate to ob ject oriented programming The first educational cycle 180 lessons includes designing uncomplicated applications and implementing them applying the standard procedures of implementation testing and documentation The second educational cycle 160 lessons includes designing applica tions with database connectivity and developing testing and documenting them with J ava according to the standards of object oriented program ming 2 Cognitive Load Theory 2 1 What cognitive load theory says and what it implies for instructional mate rial and design For a detailed 25 pages overview over it see Cooper 1998 and there the sections Suggested Readings and References What It Says According to cognitive load theory the key learning activities are schema acquisition and automation of their usage After enough training acquired schemata are stored in long term memory They allow high cognitive per formance with a very limited working memory But under conditions where multiple elements of information are interacting we have to com prehend and learn them at the same time Such material produces a high cognitive load by itself intrinsic cognitive load The instructional design may add to the cognitive load extraneous cognitive load As a rule of thumb the working memory is limited to between 5 and 9 elements If the material itself is not highly interre
64. d great success with beginning students trying to learn to program People in this business have a narrow schedule Therefore could not get any feedback in this short time elapsed since have set up a first pre release with some scenarios 1 2 Four Improvements of Roboworld Compared to Karel The second reason is in comparison to Karel added three enhance ment that think are crucial for the effectiveness of a microworld as step pingstone into object oriented programming Firstly elements to emphasise the idea of collaborating objects These elements are 1 the instantiation tool 2 the tool that lets user operate the robots manually to test single operations 3 attributes that lets ro bots remember each other and build associations and 4 the visual repre sentation of messages between robots See Chapter 6 Reducing cognitive load in Roboworld starting at page Secondly more compatibility with J ava use a simplified J ava code not a mixture of J ava and C There are also details related to J ava The 96 Chapter 9 Overall conclusion robots identification class and serial number is similar to J ava Positions and directions use the same logic as J ava s class Graphic Thirdly elements to support the Unified Modelling Language UML The UML is important to get a transfer effect from the microworld to other design tasks Without the students ability to coordinate different sign sys tems suc
65. d level Operations are consumeFuel and fill Even with little programming know ledge learners may set up Fig 6 statechart diagram of a fuel tank the code for the fuel tank and see the tank in action later in the course Filling do fillGas Ready do consumeGas Static Diagrams Static diagrams such as class diagrams and object diagrams are the most abstract to understand They only seem to be easy for experienced pro 42 5 4 Chapter 4 Existing solutions to overcome the problem of cognitive load grammers because they hold about the same information as entity relationship diagrams in database design and because they are close to object oriented code But without understanding object oriented program ming these diagrams reflect a lot of concepts of object oriented pro gramming that the learner does not know yet Books therefore use metaphors to explain the concepts It seems unlikely that understanding these metaphors really helps understanding object oriented programming It is easy to understand that there is a class category vehicles and that in this class category fall boats cars and motorcycles as subcategories subclasses No problem expect for students that do not speak English well enough to see that myMotorCycle myMotorBoat myRow ingBoat fall in one or several of these categories and that they are instances ob jects of vehicles motorcycles and or boats No problem to see t
66. e Problem The exchange of information between the object acting as client and the object acting as server is one of the main concepts in object oriented programming The client sends a request to the server by calling one of the servers operations It may send values or object references as argu ments when calling an operation The server object uses the arguments within the called operation The called operation may return a value or object reference Also as this seams to be the same as calling a procedure in procedural programming there are elements that add complexity The called object the server may be the object itself but it may also be another object This other object is defined in a different class Therefore there are more elements to be remembered at the same time than in procedural program ming The split of attention towards two files two classes is inherent to the call of methods There are some existing solutions that address this problem Solution Procedural Programming at First Procedural programming is basically equivalent to object oriented pro gramming concerning procedure or function call and return value This justifies teaching this part of procedural programming first This often means to teach method calls within the main method of a class Be cause using the main method in teaching is the most common tech nique of teaching procedural programming first in J ava After the sche mata of me
67. e developer after 6 months of education and training This involves the teaching of very com plex concepts and a huge amount of procedural and factual knowledge We tried several approaches to achieve this goal The main problem was to reduce the amount of new information presented at the same time that means the cognitive load We found that there is at least in German no appropriate material available Although there have been very interesting techniques used in education and training the problem is that most of them are not well documented Our task designing a short course in J ava is quite frequent Therefore this thesis is of high practical value It discusses the problems we encoun tered and analysis solutions and material to work around these problems It contains material and techniques we used It discusses our experiences Introduction and may give some hints for teachers to improve the teaching of object oriented programming organized the material as follows Chapter 1 explains the problem of cognitive load and the reason why it is higher in a J ava short course than in a course for Pascal or Basic Chapter 2 analyses the impact of the paradigm shift from procedural pro gramming to object oriented programming Chapter 3 discusses three problems in J ava education that are very impor tant in practice The findings in this chapter were used for improvements in the microworld Roboworld Chapter 4 analyses di
68. e missing knowledge of design pattern is reported by Fowler 2000 chapter 2 6 see text in box as one of the main problems in project teams Hunt 1998 p 16 explains some of the draw backs of poor object ori ented design he explains especially the problems of inheritance Inheri tance can reduce comprehensibly of code extremely To revise the se quential execution of code the developer has to look up methods in dif ferent classes The cognitive load of this job is extremely high If the de sign is poor the only way to solve problems of this kind is refactoring Unified Modelling Language UML as a Mean to Understand the Application Programming Interface API Without understanding design patterns the student will have difficulties to understand large parts of the application programming interface The J ava API uses often aggregation Students who know the underlying concept of aggregation will have less problem to use these parts of the API They 88 1 3 1 4 Chapter 8 Supporting the Unified Modelling Language recognize the pattern and can make use of its schema For instance knowing the schema chain of responsibility that is used for input and output streams with J ava reduces dramatically the cognitive load when learning about streams If can tell a student that input and output uses chain of responsibility he or she will have much less problem to use the API classes to set up input and output procedures Th
69. e topics Besides Bergin s description of a microworld that is discussed later this is the only book that complies with the implications of cognitive load theory A tre mendous rating of this book by amazon com s readers shows some evi dence for the validity of cognitive load theory There is a draw back to the Spiral approach in general It needs a lot of planning and elaboration for the teacher writer King needed fore years to do the job properly As J oseph Bergin 2001 emphasises This pattern the Spiral approach cannot be used in a small way A commitment needs to be made to it If this is not possible or desirable avoid it entirely 5 Teaching Object Oriented Thinking with UML Firstly 5 1 The Unified Modelling Language UML is a way to visualise object oriented problem solving and design To these methods one can also count the Class Responsibility Collaboration Cards CRC Cards CRC Cards are an entry level to both the static UML diagrams like class dia grams or the dynamic diagrams like statechart or collaboration diagrams Class Responsibility Collaboration Cards CRC Cards Kent Beck and Ward Cunningham presented CRC Cards first at the OOP SLA 89 Conference Beck and Cunningham 1989 They write The most difficult problem in teaching object oriented pro gramming is getting the learner to give up the global knowl edge of control that is possible with procedural programs and rely on the local knowledge o
70. ect oriented programming have different key concepts To reduce redundancy that means unnecessary cognitive load we have to check whether this key concepts of procedural pro gramming are needed for object oriented programming Key concepts of procedural programming are control structures like itera tion and conditional branching recursion modularisation and side effects Conditional Branching Conditional branching is a main topic in procedural programming Writing Nassi Shneiderman diagrams should help to avoid spaghetti code for com plex tasks A lot of effort in design and testing is made to get the branch ing right IF system Linux True False IF system Mac True False IF system Window s95 draw LinuxButton True False draw MecButton draw Window s95Button draw Window s3Button Fig 3 Nassi Shneiderman diagram for nested if statements Object oriented programming does not make much use of conditional branching because it uses a much more powerful tool to create diverse behaviour polymorphism Let us study for example the user interface Our application may run on Linux Mac Windows 3 x or Windows 95 In a procedural program a global variable would be set in the beginning due to the system the pro gram is running For instance system Windows95 Later we would check for this variable like Linux drawLinuxButton Mac drawMacButton
71. ects of the basic classis without referring to the class In this case the program looks for an attribute or operation first in the static object of the current type of the variable that refers to the object then in the static object of the parent class of that type then in the static object of the parent s parent class and so on In the example above inside of object 11 a CurrentAccount TYPE refers to TYPE in the static object CurrentAccount that is 17 and nextNr to the static attribute nextNr in the static object Account 22 5 6 Chapter 3 Key problems of teaching object oriented programming Conclusion Static elements augment complexity They are needed in a normal learning environment but are unknown in microworlds Using microworlds de creases the cognitive load therefore 6 Collaboration and Encapsulation Working with Object References or Pointers in Messages Operations 6 1 6 2 6 3 Description of the Problem What is the kernel of object oriented programming In object oriented programming you think of small units objects that do a small part of the job Every single operation is trivial The complexity lies in the collabora tion of all the objects instances of these classes You may discuss this problem from the point of view of program design then you see it as a responsibility collaboration problem you may define it as the technical goal of encapsulation to get small and stable interfaces Sch
72. efore often a high amount of background information is needed Some on this information can be found in the text Advantages of this Approach There is often a quick practical success If the new information involved in the model stays small and the background information covers what is new for the trainee this approach is the choice For instance if the trainee understands the basic concepts of a graphical user interface and its im plementation in swing he or she can easily use most elements of the swing package with the help of the J ava tutorial Trainees learn to read manuals and to read and adapt code examples This is an important technique in object oriented programming J oseph Bergin 2001b points out in his pedagogical pattern Read Before Write You are teaching an elementary course that has a strong pro gramming or design component You want to help them learn to eventually create large and complex programs Creating any thing is hard work even for the skilled Novices on the other hand lack these skills However as with natural language stu 35 3 5 3 6 Chapter 4 Existing solutions to overcome the problem of cognitive load dents have an ability to read and understand larger artifacts than they can be expected to create They can also learn about structure scope and aesthetics from reading great works In an English course for example students read and analyze Shakespeare s plays but are not expected
73. ere are only four items of know ledge needed besides this schema to do the job Difference between Stream and Reader Writer difference between source and object stream difference between input and output and that you usually set up a chain of responsibility of one source stream and one ore more object streams Not knowing the design pattern might be what overloads the working memory and hinder learning Is the Visual Representation Needed Theoretically design patterns can be learned without visual representa tion The visual representation of concepts and schema is not some aid that is self explaining It is something we must learn if we will use it Du val 1995 made extensive studies about this fact The Unified Modelling Language UML does not use a lot of semantic elements but other system to visualise complex facts use them neither What UML makes difficult is the syntactical variation of its signs in rather large number of diagrams Diagrams that are similar in what they show but largely different in the point of view they are representing it For in stance an objects diagram a sequence diagram and a collaboration dia gram show all objects in collaboration The objects diagram shows that objects are collaborating but not when and how the sequence diagram emphasises the sequential execution of the collaboration where the verti cal axis is the time axis the collaboration diagram displays the same but uses sequent
74. es 2 6 Identifiers 2 8 Con stants 3 Classes and Objects Declaring instance variables in 3 3 Classes Declaring instance methods method overloading con structors in 3 3 Classes 3 5 Calling Instance Methods 3 9 J ava s String Class Common Methods Chaining Calls of Instance Methods 3 4 Creating Objects 3 7 How objects are stored 3 8 Developing a Fraction Class 4 Basic control structures 5 Arrays 5 1 Creating and Using Arrays 5 5 Using Arrays as Vectors 5 6 Using Arrays as Databases 5 7 Arrays as Objects 6 Graphics 6 1 Creating a draw ing 6 4 Combining text with graphics 6 2 Drawing in colour Construct a Color object 6 3 Displaying text Construct a Font object 6 2 Drawing in colour 6 3 Displaying text 6 4 Combining text with graphics 7 Class Variables and M ethods 7 5 Class Variables 7 1 Class methods versus instance methods 7 2 Writing class methods 7 3 The Return statement 7 4 Parameters 7 7 Writing helper methods 7 8 designing meth ods 10 4 The this key word 8 More Control structures 8 1 Exceptions 9 Primitive Types 9 1 Types 9 2 Integer 9 3 Floating Point 9 4 Char 9 5 Type Conversion 39 Chapter 4 Existing solutions to overcome the problem of cognitive load Difficult topics of object oriented programming Chapters in King s textbook Common topics for str
75. etters Therefore refer to columns by number not by letter This way students can add up or discount them Back to Code Editor add one beeper Fig 16 Panel for changing the microw orid 3 2 More Functionality More functionality will be added later to this panel Drawing Walls from point to point removing all beepers setting a predefined amount of beep ers setting an infinite number of beepers are all features that will be added later 3 3 Better User Interface The user interface should be improved as well The solution now is quick and efficient But know setting up a world with icons and by drag and drop would be state of the art today Also this solution as it is does not support the subject predicate logic of graphical user interfaces intend to make later a user interface where the options work like painting tools 3 4 Conclusion did not invest much in the set up functions of scenarios As this is some thing simple it should not do any harm 4 A Panel to Manually Instantiate Robots and to Call Up their Methods 4 1 Motivation for this Feature The existing microworlds use a main task that calls the other methods of the hamster or robot Karel uses a static task which instantiates one or several robots In the Hamster Model the robot has been instantiated already by clicking An instance method main is triggered when the user chooses to run his solution For me both solutions seem not very
76. ey should construct the interaction Tell them for instance that they should find a way that all persons objects in volved in the interaction have equivalent tasks to do To visualise parameter passing use envelopes and paper instruct train ees to pick a Sequence number for any object created The trainee writes the number of the object that receives a message on the envelope He writes on small pieces of paper first the name of the operation then the value of the first argument the value of the second argument and so on The trainee puts the pieces into the envelope They should do so even with messages to this The pieces of paper inside the envelope make up the signature of the operation The receiving objects will choose the ap propriate method based on the signature and use the values passed to complete the method The envelope will be returned to the calling object person when the operation is completed The envelope will be returned void or with a piece of paper with the return value in it This role play helps the trainee to build up the schema of collaboration without unnecessary additional information such as Unified Modelling Language diagrams or code syntax Conclusion Collaboration technically aggregation and encapsulation in point of view of design is one of the key concepts of object oriented programming With role plays it can be teached avoiding cognitive load 7 Polymorphism Types and Overwriting Meth
77. f ter some seconds or minutes of reflection he asks for the decision If trainees do not agree about right or wrong the group discusses the solu tion 12 5 Group Activity Black Sheep Black sheep is similar to imperator The stimulus is not one code example but different solutions One of the solutions the black sheep is wrong The trainees have to decide which one As in imperator in case of disagreement the solution is discussed 12 6 Individual Activity Flash Cards Flashcards with multiple choice questions are possible The problem is that the trainee might remember the right answer by hard instead of rec reating the answer by reflection That means he remains on the low cogni tive level of recall instead of applying basic knowledge to a new situation The creation of flash cards by peers and exchanging this flashcard can overcome this problem 12 7 Creating own Examples The trainer can ask the trainees to invent their own examples for imper ator black sheep or write their own flashcards Finding examples is on the same cognitive level than applying basic knowledge to new situations See 59 12 8 Chapter 4 Existing solutions to overcome the problem of cognitive load the evaluation of Metzgere a 1993 p 72 based on the taxonomy of Bloom 1956 Conclusion Cognitive load can be reduced by several offline activities Some of them may apply to distant learning some are designed for group activities Buildin
78. f cognitive load e The popular German online documentation Self ava Schr ter 2001 uses Cars and different types of cars as a metaphor when explaining inheritance Similar Niemann 2001 p 71 uses vehicles in general di vided into ships and land vehicles e Bishop 1997 uses Nature as basic type for Birds Trees and Animals with subtype Carnivores and Herbivores e Goll 1999 uses SteamBoat p 38 Person and Student p 40 Ma chine with subtype FaxMachine Computer p 44 e Lemay 1999 uses first trees like Bishop does but switches to mon sters with subclasses FlyingMonster and WalkingM onster e Bergin 2000 in his An Object Oriented Bedtime Story uses the metaphor of people doing services for other people People are objects of different types Bergin s Bedtime Story is especially interesting be cause in his metaphor he uses aggregation and object s interactions He explains the object s role as client a patient and server a doctor About Effectiveness of Metaphors Iding 1997 p 249 reports based on several studies that analogies foster learning Analogies can be good if students receive information about their limits This lets students better map the parts of the metaphor that are applicable to the new situation Not surprisingly for semiotic researchers she reports three things 1 metaphors do support the transfer of knowl edge 2 it is preferable to use several analogies instead of one
79. f objects to accomplish their task It is in this context that we will describe our perspective on object design its concrete manifestation CRC for Class Re sponsibility and Collaboration CRC Cards are used as follows 1 You write down on a paper card A5 or smaller i e 10 15 cm the classes you find relevant to your project in top For instance in a project for a bank Account Customer Current Account Value Performance Shares Portfolio might be things you find relevant Beck and Cunningham 1989 mention a banking machine and suggest in their solution Account Transaction CardReader Dispenser RemoteDataBase Event Interface FSM Screen and Action 2 On the left hand side of the cards You write down the tasks responsi bilities you think are natural for this class For an account natural respon sibilities might be deposit withdrawal check current value calculate in terest show interest rates history show history of transactions 41 5 2 5 3 Chapter 4 Existing solutions to overcome the problem of cognitive load 3 Opposite on the right hand side you make a note that tells which classes work together to accomplish this task collaboration For instance to show the history of an account you need all the transactions on this account You do not mention collaborations if a class can fulfil some task without another class but may work together with another class For in stance Beck and Cunningham 19
80. f the J Unit distri bution doc cookstour cookstour htm available at ftp w ww armaties com D home armaties ftp T estingF ramew ork J Unit Bergin Stehlik M Roberts J Pattis R 1997 Karel A Gentle Introduction to the Art of Object Oriented Programming J ohn Wiley and Sons Inc New York online http www csis pace edu bergin karel html Bergin 1998 Teaching Object Oriented Analysis and Design in CS 1 online http www csis pace edu bergin OOAD html Bergin J 2000 An Object Oriented Bedtime Story published online http w ww csis pace edu bergin ava OOStory html Bergin 2000a Why Procedural is the Wrong First Paradigm if OOP is the Goal published online http www csis pace edu bergin papers W hynotproceduralfirst html Bergin 2000b Objects in Operation published online http csis pace edu bergin ava oopanim html Bergin 2001 Fourteen Pedagogical Patterns published online under construction http www csis pace edu bergin PedPat1 3 html Bergin J 2001a A Gentle Introduction to the Art of Object Oriented Programming in J ava not published but online under construction http w ww csis pace edu bergin Karel ava2ed Karel J avaEdition html Bergin 2001b Some Pedagogical Pattern online http w ww csis pace edu bergin pattern few pedpats html Bloom B e a 1956 Taxonomy of Educational Objectives The Classi fication of Educational G
81. fferent approaches to overcome the problem of cog nitive load It checks whether experience can be explained by cognitive load theory Chapter 5 analysis existing microworlds as a promising way to overcome the problem of cognitive load in an elegant way A way also that allows teachers to introduce important topics such as problem solving and soft ware design very early in a course Chapter 6 outlines and describes a new microworld called Robow orld especially designed to teach J ava in a short course This chapter is to prove that the cognitive load is heavily reduced and that there is enough similarity that Roboworld can serve as a steppingstone to real J ava pro gramming either to the programming of Applets or of J ava applications Chapter 7 discusses the metaphoric power of Roboworld so it can be used to explain basic concepts about the development of software Chapter 8 explains the importance of sign systems such as the diagrams of the Unified Modelling Language UML for the development of software and how Roboworld supports these sign systems Chapter 1 Cognitive load in a Java short course Major objectives in a J ava short course are mostly higher cognitive activi ties For such activities the cognitive load theory might be valid The level of interactivity of the elements is extremely high 1 Major Objectives in a Java Short Course For the half year short course to educate junior software developers the
82. from keyboard or output to screen import java io class provides basic input and output Services and possible to halt execution for some time public class Services execution sleeps for a second static public void sleep for shorter or longer sleep times sleep 1 0 call method sleep double sec here after execution sleeps for number of seconds param sec number of seconds static public void sleep double sec try should be grater than 0 01 on most systems Thread sleep may thorw the InteruptedException Thread sleep int catch InterruptedException e sec 1000 The InterruptedException must be caught even if you do nothing in case of a Interruption write a line of code to standard output This operation is called writeLine because this complies with java s naming convention static public void writeLine String s write some text to standard output System out println s public static void write String s promts for input and gets it System out print s System out refers to the standard output the screen the screen Input Output Exceptions that can occure with any access to your computer are caught handeled within this method param prompt the prompt to be presented to the user return the input as String public static String readLine String pmt for decent
83. g Firstly there are only advanced topics of procedural programming that are not relevant for object oriented programming So learning procedural pro gramming with J ava or C gives a good base for programming with J ava After the student is familiar with the basic principles of J ava there is less cognitive load when moving to object oriented afterwards The highest rated book written in German for learning J ava Boles 1999 fol lows this approach Even adepts of object oriented programming suggest this book for education at technical universities before plunging into ob ject oriented programming with a book that gives a sound technical back ground for object oriented programming Gool 1999 Also if you take a closer look on most basic books about J ava programming you find that they cover elements that procedural programming and object oriented pro gramming have in common They program procedurally inside the class operation main ignoring most of object oriented concepts Availability of material and workforce Secondly and for long time most important you can entirely rely on mate rial that you used earlier for teaching a procedural language like Pascal Fore instance if you do not have experienced object oriented program mers as teachers and sufficient learning materials at hand you run into troubles with a course for object oriented programming acknowledge that myself have been working with procedural programming for ye
84. g schemata with such activities is often more effective than online problem solving At least there is less risk that new items of information supersede working memory 13 Chapter Summary 13 1 13 2 May we relay on experience and estimations Don t we need proof Estimations and Experience from the Analysis of Existing Material A lot of experience on teaching J ava supports cognitive load theory There is no proof of the correctness of cognitive load theory But the cognitive load theory seems to be an appropriate model for the evaluation and de sign of highly interrelated topics like teaching object oriented programming with J ava Books and classroom activities could be designed to be more effective Planned books scripts and classroom activities should be checked for cognitive load Cognitive load theory may give us hints to improve teach ing and to design improved educational material Among the most efficient approaches to reduce cognitive load there are e Microworlds e Books that use a spiral approach e Reinforcing knowledge acquisition by flash cards mind maps and short review questions e Learning to apply knowledge to code by checking code examples ei ther in a textbook on a flash card or in a group activity e Fixing and improving code while focusing on specific problems and small tasks Do We Not Need Proof mentioned in the beginning the metaphor of a racing car where behav iourism cognitivism and c
85. g there are two kinds of variables global vari ables and local variables They share the same name space The end of block limits the scope of local variables and they may hide global variables or local variables of an outer block In object oriented programming there are some other components of com plexity added Firstly there is the name space of the variable Every object has its own name space Therefore different variables with the same name are rele vant in many situations Trainees have to learn that assigning a value to a variable does not mean that every variable with that name holds now that value Plus he can use the same name in different classes for different 16 1 4 1 5 Chapter 3 Key problems of teaching object oriented programming values and even different types When you work with variables in object oriented programming it is very confusing for learners that the same name of a variable holds different values information and that the same data information is stocked in variables with different names when being sent from object to object Secondly objects and classes share name spaces Inside a method we can access the variables of the object called the object s fields without referencing the object We can also refer to the object with the key word this Sometimes we have to refer to it because a local variable has the same name as the object s field Resulting in code like this balance b
86. g to work out with the students a toolbox a set of basic classes for their own work during the course Such input or service classes could be part of such a toolbox While giving the trainees as an exercise the task to work out the input or service class they used in the beginning of the course you avoid certainly the impression to have learned J ava gently and not J ava The Unit Testing Approach More demanding is the use of unit tests In a unit test you test the func tioning of all singular methods in a class Does the method meet your ex pectation its specification You send to standard out all information about malfunctioning of methods The framework J unit helps to set up unit tests Unfortunately this instrument is a bit to complicate for novice user to use it In a course with intermediate students you may use it It is 27 Chapter 3 Key problems of teaching object oriented programming very helpful to visualise what design by contract specifications and inter face means With the unit tests you verify by assertions that specifications are met You make tests to verify whether preconditions and post conditions are met Instead of using the framework J unit one can easily set up his own unit tests A class with a main procedure that instantiates objects and calls up the operations of these objects is sufficient Novice programmers will send a feedback line to standard out under all conditions Experienced pro grammers w
87. ginners 2 The experience that learners were not able to learn the diagrams with out the background knowledge of an object oriented programming lan guage 5 10 Starting with CRC Cards and Unified Modelling Language in the Light of Cognitive Load Theory CRC Cards have only three semantic elements and the procedures to use them can be acquired quickly The usage goes step by step Important to note you use them in a goal free process The first instruction is to write down objects classes Then you think about their responsibility Then you think about with whom the should collaborate to fulfil this task Therefore cognitive load is low There is no split of attention no goal and no redun dancy The learners can play the interactions so that a high degree of in volvement and learners activity is guaranteed Bergin 1998 and my own experience are good what gives some support to cognitive load theory The charts of the Unified Modelling Language show more but not an overwhelming amount of semantic elements Our experiences were good with statechart diagrams fair with static diagrams objects and classes and mixed with dynamic diagrams like sequence and collaboration dia grams The latter may be explained with the redundancy when introducing two types of diagram for the same purpose in the same cycle of a course The better experience with statechart diagrams may be implied by the fewer interacting elements Statechart diagrams show only
88. h as Robots interactions J ava code role play with CRC Cards design by walking around collaboration diagrams sequence diagrams class diagrams there is less transfer of knowledge As this is true for mathematics it must be true also for computer science because the un derlying problem of knowledge and comprehension is the same See Chapter 8 Supporting the Unified Modelling Language starting at page 8 2 Conclusion from this Thesis 2 1 The question asked in the beginning was whether cognitive load theory can be this rote rules to apply as Wilson 1995 mentioned Something used like the four factors for readable German text in Langer 1981 In this case should have been able to analyse and to improve existing in structional material Analysing Existing Instructional Material analysed existing methods to get around problems encountered while teaching J ava rated the cognitive load not distinguishing between in trinsic and extraneous cognitive load used my intuition to do so But my intuition of cognitive load could be represented in a scale similar to the scales used by Langer 1974 It might look like this Heavy cognitive load Low cognitive load e unknown items e known items e heavily related items e items can be consid e several sources of in ered separately formation needs split e one source of informa ted attention tion e redundant items without e no redundant items or emphasis
89. hat a car is a composition of motor trunk passenger s cell and 4 wheals etc Vehicles abstract turnLeft turnRight accelerate stop Sailing Boat Sail Cars Motor e e Rudder wheel Brake Fig 7 class diagram figurative example but assigning behaviour does not work Problems start when transferring to real object oriented behaviour You see arise big question marks when you explain that all vehicles must know the operation turnLeft and turnRight Or when you explain that they use different methods to fulfil these operations The main benefit of static diagrams is that people learn the vocabulary well But still without coding the transfer from static charts to code and the real understanding of the behaviour of objects in object oriented pro gramming is not sure at all Other Diagrams It is a little dangerous to use other diagrams to visualise elements of J ava code J udy Bishop 1997 tries it in here book J ava Gently Some read ers find her specific object modelling technique fine because the diagrams 43 5 5 5 6 Chapter 4 Existing solutions to overcome the problem of cognitive load give them an overview of the example programs at one glance For most others they mean another burden added to the heavy cognitive load J udgement of this A
90. he knowledge needed for object oriented program ming most likely 1 Practical Background The programming language J ava is widely used for introducing novice learners to programming Also it is used to teach object oriented pro gramming to expert procedural programmers There are several reasons for this Kim N King probably one of the best teachers in this field writes in his book J ava Programming From The Beginning King 2000 p xvii When J ava appeared in 1995 immediately noticed its poten tial as a language for beginning programmers J ava satisfies today s need for early instruction in an object oriented lan guage while avoiding the complexities of C At the same time J ava is similar enough to C to serve as a stepping stone to that language At my institution J ava is the first lan guage introduced immediately followed by C With no pointers to cause problems J ava programs are immune to those frustrating crashes that are so common in C If a J ava program does encounter an error at run time the inter preter provides a stack trace that can often pinpoint the prob lem And last but not least the software needed to write and execute J ava programs can be downloaded from the Web at no charge At the institution for adult education where teach J ava we have very ambitious goals People without any background in information technolo gies should be able to start a job as a junior softwar
91. he microworld and can be seen 1 4 Conclusion The authors main motivation is to introduce problem solving and program design early in the teaching process A long tradition of LOGO program ming with children and students education with worlds for Pascal and other procedural languages was successful to do so Reducing cognitive load is part of this approach Especially Boles is aware of the importance to reduce the number of concepts that need attention at the same time 2 Microworld Problem Solving and Object Oriented Design As problem solving and design is the main field of interest We take a look at what microworlds may provide 2 1 Software Development is a Problem Solving Process Dietrich Boles 1999 chapter 3 Programmentw icklung p 35 and J o seph Bergin 1997 chapter 3 8 Tools for designing and writing robot programs both are driven by the idea that the trainee should learn from the very beginning that software development is a problem solving proc ess He or she should learn not only bricks of J ava but permanently ex perience programming as a process of problem solving The trainee should learn the techniques to do it in the beginning and apply them throughout the entire course 63 2 2 2 3 2 4 2 5 Chapter 5 Existing microworlds for teaching J ava Scenarios Used to Teach Software Development J oseph Bergin uses two basic problems to teach problem solving with object oriented pr
92. he server must rely on other objects to help it fulfils the service request It then itself acts as a client to these other objects which act as servers for it Control returns to the message sender even if no information is returned Bergin displays 2001 b an animated GIF that gave me the initial idea for the visualization used in Roboworld Conclusion Despite the possibility of further improvements believe that the graphical and textual feedback helps to acquire schemata of collaborating objects Manual instantiation of robots learn mode and the possibility to play and experiment goal free around with robots might reduce cognitive load Most important as believe is the graphing of messages between robots There the most important happens therein feel lies the heaviest cogni tive load 6 Define Attributes that Reference Robots and the Instantiation of Robots within Program Code 6 1 The association between objects is done by attributes This basic concept should be implemented in the microworld too Existing Worlds Existing worlds are not object oriented Hamster World use only local variables or four predefined attributes Karel or are written in J ava classes J Karel 77 Chapter 6 Reducing cognitive load in Roboworld 6 2 Motivation As analysed in previous chapter attributes also called fields or instance variables are so important to organize collaborations plus are extremely interrel
93. his has some of the same goals as Mistake though it is ap proached differently Here we find errors In Mistake we make spe cific errors This pattern is a way to achieve Read Before Write For all this ideas teaching pattern Bergin explains when and how to use them An example of a FixerUpper could be a class Person where the at tribute for the last name is missing The student has other attributes with their query and update methods as worked examples already written in the class Now he can add the attribute for the first name with the re lated methods with very little cognitive load Read Before Write versus Hiding Details Bergin emphasises that learning to read code before you write code is very useful in teaching object oriented programming An adverse experi ence of J ava trainers is that students loose a lot of time studying code details they do not understand yet Cognitive load theory suggests rather hiding details that students do not understand completely because they add to the cognitive load Experience with language teaching may give some idea why it may be all right to reveal details The technique of Total Immersion Listening without understanding firstly before taking that means the way children learn languages is a good way to learn languages It might be a good way to learn computer languages too The diverse experiences depend most likely on the material you provide If the material is excellent T
94. hort course Reason for the Complexity of Object Oriented Programming One main problem for teaching is the complexity of object oriented pro gramming You do not understand the code of the most simple J ava appli cation or applet Hello world as long as you do not know very complex concepts of object oriented programming J ava is an ingenious language but you need a lot of J ava specific knowledge even for the most basic tasks For instance the Hello world Application that a teacher in general must use needs In a procedural programming lan In an object oriented programming guage such as Pascal language such as J ava e A simple program structure e A simple class structure e The predefined procedure e The definition of a static method w riteln main e The string constant Hello e The string object that contains world Hello world e An array of objects of class String even if this argument ar ray is not used e The class System because this class contains a reference to the standard output in the static at tribute out e System out refers to an object of class PrintStream e This object s operation print is called with the argument String i e System out printIn String e The argument String is upcasted automatically to argument Ob ject e The operation printin Object of PrintStream calls the operation toString from class String to write the object to the st
95. ial numbers for the messages sent A small but nasty problem is that for some details type identifier UML deviates from the syntax of J ava For instance ballance int in UML is written int ballance in J ava syntax And it uses other names for in stance attributes are called fields in J ava Semiotic Research on Mathematical Sign Systems From the semiotic point of view the Unified Modelling Language is a sign system Following the argumentation of Duval 1995 the results from the extensive research for sign systems in algebra and geometry must be transferable to the Unified Modelling Language Duval 1995 p 75 explains the crucial points based on studies of mathematics 1 Even now the teacher uses different sign systems regis tre de repr sentation students will not be able to coordinate them 2 Hence most of the time learning will take place only in one sign system 3 Most important This understanding in only one sign system com pr hension monoregistre is a major handicap as soon as students leave the context in which learning took place most of them will be not able to use their knowledge however they actually know it Duval concludes 1995 p 76 89 1 5 Chapter 8 Supporting the Unified Modelling Language Plus g n ralement une compr hension monoregistre est une compr hension qui ne permet aucun transfert Seul une com pr hension int grative c est dire une compr hension fond
96. ic cognitive load is reduced dramatically The trainee can focus on the algorithmic and design schema he has to learn The immediate visual feedback discharges the brain from the task of relating unintended results to coding errors Karel with its C like code adds some redundancy The display of the executed code not on the acting robot or hamster but in a separate window does split attention Conclusion By dramatically lowering the amount of intrinsic cognitive load mi croworlds seem to be the only way for a quick introduction to the key ideas of object oriented programming Still considering the cognitive load theory the design of existing microworlds needs improvements 10 Programming in Pairs 10 1 Two persons working at the same computer programming in pairs or pair programming is used in the software industry to improve efficiency It has a teaching coaching effect that might be used for training too Definition of Programming in Pairs in Software Industry Programming in pairs is described in the web see http c2 com cgi w iki ProgrammingInPairs 55 Chapter 4 Existing solutions to overcome the problem of cognitive load This was called aa In Pairs in its first published description by Limtoplien see Historical Note below It s hese days notably by Context You have several people working on a project Every one S received the basic training necessary to do the job Some more or le
97. ies between Learning Theory and Instructional Design paper presented at the meeting of the American Educational Research Association San Francisco March1995 Available at http w ww cudenver edu bwilson 109
98. ight at the beginning For me the collaboration of objects is as crucial for the paradigm of ob ject oriented programming as polymorphism is If you check for instance the design patterns in the famous book Design Patterns Gamma E and others 1994 you will see that in most patterns collaboration of several objects and sub typing goes hand in hand So if there is a serious criticism about Karel it is the fact that it does not do more effort in teaching how to set up aggregations of Robots that work together User Feedback about Working with Microworlds The feedback for the German version that covers only procedural pro gramming is enthusiastic on www amazon de The feedback for the Eng lish version is mixed on www amazon com Both feedbacks are not sig nificant only 3 4 ratings Obviously the English version with Karel did not meet the reader s expectations completely Despite the German Hamster Model only covers procedural programming it was highly estimated The enthusiastic reader comments prove that the approach has been appreciated The English Robot microworld shows that you can teach also object oriented programming with microworlds Some shortcoming of the book Karel does not lay within its general approach The book is not as well edited as the German book about the Hamster Model Examples are lengthy The visual organisation of the book is fair but not good or excel lent read some comments criticizing th
99. ildt 2001 p 11 identifies Encapsulation as the first principle of object oriented programming see it more pragmatically for beginners The objective is to be able to set up collaborating objects and this means to understand how object know about each other and how they refer to each other It means to know how such references are set up in a program Because collabora tion is only possible if several objects know each other In the view of object oriented design collaboration is often seen as aggre gation Instead of defining one object that does the entire job you design several objects who work closely together There may be one object that acts as a contact to the outside of the group and receives all messages first But then this objects sends messages to other objects that are closely related to it For the beginner aggregation or collaboration is difficult to understand and even more difficult to set up and implement There are several ideas to help beginners with setting up aggregations of collaborating objects Visualization of Collaboration in Class Diagrams The association in class diagrams are a good visualisation of the relation ship between objects Students understand usually associations in class diagrams But the transfer from drawn association in a static diagram to code is not evident You have to teach how to transform associations to code For instance to teach collections like Vector does not help There is
100. ill do so only in case of failures to reduce output Unit testing is not something trainees do without instructions Testing must be part of programming permanently This unit testing gives trainees the feedback they need They will spend less time with unnecessary func tional testing That means with tests of entire use cases through the graphical user interface 8 7 Conclusion Programming J ava s user interface is too difficult for beginners Avoiding graphical user interfaces in the beginning and providing classes that help with input and output lower cognitive load dramatically 9 Richness of Contemporary User Interfaces There are ample of components in contemporary graphical user interfaces For instance with Swing all elements of a modern graphical user interface are available Avoiding teaching all elements but concentrating on the de sign aspect of the user interface helps learners 9 1 The Use of Aggregation in J ava J ava does not provide multiple inheritance Instead you use aggregations For instance in the graphical user interface of J ava Every component has its graphics representation on screen associated It is not a subclass of Graphics The missing multiple inheritance in J ava is the reason for this structure Every container has its LayoutManager Other than the relationship be tween component and graphics this structure allows to combine Container and LayoutM anager dynamically Also you can extend the abil
101. input java uses a chain of responsibility nputStream System in is in contact with your computer and is responsible for getting Keyboard input a 8 Bit Ascii the InputStreamReader transfers 8 bit ASCII Code to 16 bit Unicode the BufferedReader provides methods like readLine so you do not have to process any single character read means that the method read is called repeatedly until the line is done object I readLine lt Entire Ef Q gt br ButferdReader gt isr InputStreamReader Line lt Unicode lt ASCII InputStreamReader isr new InputStreamReader System in the constructor is ClassName InputStream nextObject InTheChainOfResponibility so the chain is constructed from the end to the beginning new BufferedReader isr BufferedReader br write pmt calls write String pmt try here after all access to your coumputers input output devices may throw a IOException String 1 T br rea dLine if 1 equalsIgnoreCase exit return 1 catch IOException e System exit 0 System in InputStream 102 Appendix B Service Class for easy input output in J ava the trown IOException is caught here return the name of the thrown exception instead of the line return e toString promts for input of a number and gets it Mal formed Number Exceptions that might occure are
102. ion 13 67 Redundancy effect 4 37 77 Reference 22 Remedial Information 70 Review questions 57 Role play 23 42 Save operating 66 Scenarios 69 Schemata 3 Schroter 33 Semiotic research 33 89 serial numbers of object 17 78 Shared name space 22 Side effect 13 55 Sign systems 89 Software development 63 Software industry 88 Index Specifications 50 Spiral Approach 38 problem solving aspect of the 40 Split attention effect 4 74 Spreadsheet metaphor 71 Statechart diagrams 42 94 Static attributes and operations 19 Static diagrams 43 Static elements as a Special object 20 Static object of the class 21 Super class 79 Sweller 60 61 Swing 28 System out printin 16 26 Technical explanation for pointers 17 Template class 78 Test Class 49 Test suites 49 Theoretical background 32 Transfer 65 Type safety 81 Unified Modelling Language 41 90 Unit testing 27 Use case diagram 7 Variables 81 82 as novices problem 15 While statement 66 Wilson 5 96 Worked example effect 4 36 48 49 61 working memory 3 WYSIWHa What you see is what happens 63 WYSIWiG 63 106 Bibliography Beck K Cunningham W 1989 From the OOPSLA 89 Conference Pro ceedings October 1 6 1989 New Orleans Louisiana And the special issue of SIGPLAN Notices Volume 24 Number 10 October 1989 http c2 com doc oopsla89 paper html Beck K Gamma E 2000 J Unit A Cook sTour part o
103. ities of all subtypes of containers frame windows and dialog windows panels by defining new types of LayoutManagers Therefore there are good reasons to prefer aggregation to multiple inheri tance There are good reasons to regard it as an advantage of J ava not to allow multiple inheritance But aggregation is difficult to understand in the beginning Therefore there is a stiff learning curve for beginners starting to early with graphical user interface programming 9 2 Other Knowledge Inherent to the J ava Graphical User Interface After the learners have acquainted basic knowledge in object oriented programming then the J ava graphical user interface is a good example for 28 Chapter 3 Key problems of teaching object oriented programming aggregation It is also a good example for other design pattern Further it is good material to work with the J ava tutorial and the J ava documenta tion In fact the graphical user interface of J ava is an excellent subject to study after the basic knowledge is safely implemented in your students So when you start teaching the J ava graphical user interface take care to explain the design pattern used for it Do not explain all the possibilities of the Abstract Window Toolkit AWT or even of Swing The trainees will not have any difficulties using them once they have understood the basic design pattern used in the Abstract Window Toolkit There is the J ava tutorial and there are ample of bo
104. ity This means no unnecessary redundancy The forth factor was redundancy added to motivate the reader For instance vivid examples questions dialog This redundancy showed a negative impact as soon as the organization of the text was not perfect Overcoming the Old Fashioned Way In practice some ideas persist a long time even in case of severe frustra tion The findings of the cognitive load theory often prove that these stan dard practices are inefficient And what is important for teachers changes do not need enormous efforts Conclusion The cognitive load theory seems to be an interesting simple and efficient tool to analyse weaknesses and design improvements in a field where you encounter high levels of students frustration 4 Analysis of the Cognitive Load in a Java Short Course 4 1 Outline of the Curriculum The objectives of the above short course were For the first educational cycle 180 lessons Knowing the structure of a J ava application Applying the basic J ava commands to write programs Using classes of the API and objects correctly And lastly understand ing the procedure of refactoring object oriented software For a second educational cycle 160 lessons Implementing database connectivity with J ava Writing simple applications that provide net ser vices Knowing sources of current information about J ava Defining soft ware specifications with Unified Modelling Language UML and imple menting
105. l the power to solve a given simple problem in a variety of ways There is no way outside microworlds to show different ways of problem solving from the very beginning Without microworlds the trainees learn in the beginning the theory about how ingenious object oriented programming is With microworlds he can use effectively object oriented programming tech ap niques with very little training King s 2000 excel wa lent book needs 443 pages before getting to the topic of sub typing And without microw orlds this is the way one should go to effectively teach it well 2 8 More Variations More Training and Transfer The teacher cans set up new problems easily In the harvest problem for instance using variations of L beeper fields can show the need for sub typing In ne PA O the basic field there is a beeper on every field o You can define fields of beepers with a beeper on Fig 13 variations of every second cell vertical and or horizontally or pales problem with two beepers on every second cell T m z T E H T u T T w ul E i EP E 2 9 Conclusion There is very little cognitive load this way the student can study and use effectively key concepts of object oriented programming like inheritance and collaboration after a very short time of training He does think about object oriented design from the very beginning without experiencing that this should be something difficult or cumbersome 3 Other Elements of Te
106. lass diagrams 23 Collaboration strategy 64 Command line interface and cognitive load 9 Common basis of procedural programming and object oriented programming 30 Communication 90 Compiler 70 Composite component 45 Conditional branching 12 Control statements in Roboworld 79 Control structures 66 Cooper 3 4 5 Counting 61 CRC Cards 23 41 Creating own examples 60 Data 84 Data input 85 Data output 84 Data storage 84 Design and implement 90 Design Flaws of the microworlds 54 Design pattern 45 88 91 Disadvantages of Existing Worlds 67 Dorig 59 Drawing diagrams 44 Duval 89 90 Eckel 13 14 21 33 34 Encapsulation 22 83 Espich 59 Event driven applications 85 Feedback 49 52 in Case of Never Ending Recursion 80 104 Index Fields 78 File handling 69 Fixer Upper 47 Flash Cards 58 60 Flow of control 63 For statement 67 Fowler 45 88 Gamma 13 45 54 88 92 Garbage collection 82 Gibbons 31 Goal free effect 4 72 Goguen 109 Goll 33 Graphical user interfaces 26 and cognitive load 9 Group activity black sheep 59 Group activity imperator 59 Hamster Model 68 Hiding details 48 Hunt 88 Iding 33 87 90 If statement 66 Inheritance 83 87 91 Input and output 26 Instance variables 78 Instances 21 Instantiating a robot manually 73 Instantiation of robots 86 Instantiation tool 72 Instructional material 97 Java 1 complexity for beginners 8 J Karel 68 Jones 63 Karel 68 King 1 27
107. lated it does not produce high cognitive load itself In this case the cognitive load added by the instructional design is not critical To conclude Learning difficulty correlates with the number of elements that must be learned simultaneously Therefore we have to study firstly how interrelated elements in the curriculum of object oriented program ming with J ava are More information can be handled when the learner can group information into larger units schemata That is when he knows most of the content and the structure of the information 2 2 Chapter 1 Cognitive load in a J ava short course For instance the text class MyClass extends JFrame public JLabel labell new Label Name MyClass means an accumulation of puzzles to the beginner The expert or even intermediate programmer will easily recognise the beginning of the defini tion of a stand alone window for a graphical user interface GUI What It Implies For material that has a high level of cognitive load by itself the cognitive load added by instructional material and course design should be as low as possible Things that add cognitive load should be avoided Tested effects of the cognitive load theory are according to Cooper 1998 The goal free effect the worked example effect the split attention effect the redundancy effect the modality effect The goal free effect is studied for mathematics In classical training exam
108. ll other objects or classes He may also call himself 44 5 7 Chapter 4 Existing solutions to overcome the problem of cognitive load Design Pattern and Member Analyse Pattern Design pattern are pat join tern that are independ aon ent from a problem do listMerrbers main and therefore can listLicendPlayers be used in different ap plications Such pattern proofed to be too ab stract for beginners Even obvious patterns Peregon Union like composite component described hasPayerLicence at Gamma 1994 p hasCoachLicence 163 are difficult to un derstand used the visualization in the book of Fowler 2000 sec tion 6 2 that shows a object diagram and the related class diagrams and asked to transfer the idea to the example of another type of organisation unions and their members The trainees had sever difficulties to do this transfer Fig 8 example of the composite component de sign pattern olympicConritiy Union frenchSoccerUnion Union germanSoccerAssociation Union fcMonaco Union fcBordeau Union fcBayernMunchen Union fcHamburg Union franzBeckenbauer Member giovanniBber Member playerLicence false coachLicence false playerLicence
109. malism And this should not be changed to avoid bringing back in cognitive load 81 Chapter 6 Reducing cognitive load in Roboworld 12 Does Roboworld Solve Novices Problems 12 1 12 2 12 3 12 4 In Chapter 3 Key problems of teaching object oriented programming pin pointed to some major problems of novices with J ava Does Roboworld help us to overcome these problems Understanding Variables in J ava Variables are very different in object oriented programming Most impor tant are instance variables They may hold values such as row column direction This values are updated and queried by methods For these up date and query operations inherited the convincing solution of Karel What Karel lacks are instance attributes called fields in J ava that hold references to other robots This very important feature to really work with collaborating robots has been added Conclusion Students can study the two major types of variables values and references to objects as instance variables fields This way hope having set a secure base for understanding variables in J ava Understanding Pointers or Object References In Roboworld students choose robots by selecting them from the list of instantiated robots In this list robots are not referenced by name but by type and number The syntactical representation of type and number is about the same as by J ava s default toString method This way
110. maps for repetitions of basic knowledge Flashcards have a review question in front and the answer to it on its back Cards should be small about 3 times 7 cm so that the question and the answer are not longer than one to three sentences Often they hold only key words The flashcards are provided by the teacher or written by the students themselves what needs training 57 11 3 11 4 11 5 Chapter 4 Existing solutions to overcome the problem of cognitive load Mind maps Mind maps hold only keywords They are a visual representation of all the nodes of the technical terms and the knowledge of a topic There is special software for mind mapping Students need instructions when they should use mind mapping for themselves Evaluation of Control Questions Flashcards and Mind Maps The knowledge training of this kind remains on a low cognitive level The trainee only has to recall what he has learned Nevertheless it is impor tant for the trainee to name things correctly to recall code elements by heart and to remember the most important problems and advantages This helps him to acquire the complex schema Every name for a nod in the know ledge tree of object oriented programming reinforces long term memory and helps to reduce the cognitive load As these techniques are integrated in a course or book it would be bare speculation to say any thing about their efficiency based on experience or reader feedback on amazon com Co
111. mer lastName Miler firstName Joe Customer Customer lastName Black firstName Nancy lastName Green firstName Harry Fig 4 classes displayed as static objects explain them that any class holds definition for two kinds of objects 21 5 3 5 4 5 5 Chapter 3 Key problems of teaching object oriented programming The Static Object of the Class From one kind there exists only one object This object is automatically constructed when the class or one of its objects is used for the first time You refer to the attributes and the methods of this object by the name of the class This object is defined by the static attributes and methods in the class definition Let us call it the static object As the static object needs no instantiation it is not correct to name it an instance of its class acknowledge that the notion of a static object proposed here is new But it is powerful and it might overcome unnecessary argumentations that static methods and attributes are not really object oriented Eckel 1998 p 162 chapter 4 writes about this issue Some people argue that static methods are not object oriented since they do have the semantics of a global function with a static method you don t send a message to an ob ject since there s no this This is probably a fair argument and if you find yourself using a lot of static methods y
112. mers in de scending order 1 flow of control 2 side effect 3 recursion 4 pro cedure call to many or not enough arguments 5 variables non unique names for global variables 6 modes of the programming environment Validity of these Problems for Object Oriented Programming According to the different paradigm most of these mistakes can not occur in object oriented programming These are side effects recursion and global variables with non unique names Flow of control and procedure call are very different in object oriented programming and cause therefore different problems As a result we can not based on this study figure out what the main problems of object oriented programming are 5 Conclusion Teachers can avoid some advanced topics like side effects extensive conditional branching recursion and modularisation in a J ava course Nev ertheless this fact does not reduce the heavy cognitive load in the begin ning of a J ava course as discussed in the previous chapter Novices prob lem studied for procedural programming give us no exact guideline for problems we will encounter in object oriented programming because the main problems of procedural programming can not occur in object oriented programming These problems are therefore studied more deeply in the next chapter 15 Chapter 3 Key problems of teaching object oriented programming There are some problems that make object oriented prog
113. might be an interesting side ef fect of Roboworld 87 Chapter 8 Supporting the Unified Modelling Language Do we need the diagrams of the Unified Modelling Language UML or do these diagrams add unnecessary redundancy If we need them how does Roboworld supports learning the diagrams of the Unified Modelling Lan guage 1 Is the Unified Modelling Language UML a Subject for a Java Short Course 1 1 1 2 Unified Modelling Language UML in the Software Industry The UML diagrams are widely used in the software industry They are used during the process of analysis The developer creates a model of the problem domain described by the problem domain expert This model is written with UM L diagrams There are design patterns that are used in any large project The developer will consider them already while he is modelling the problem domain Ig noring them results in software that is almost not manageable Grady Booch writes in the foreword to Gamma 1994 p xiii All well structured object oriented architectures are full of pat terns Indeed one of the ways that measure the quality of an object oriented system is to judge whether or not its develop ers have paid careful attention to the common collaborations among its objects Focusing on such a mechanism during a system s development can yield an architecture that is smaller simpler and far more understandable than if these patterns are ignored Th
114. n introducing concurrent states in a statechart 94 Chapter 8 Supporting the Unified Modelling Language 2 6 Class Diagrams Drawing class diagrams is also something important We can show the students that we mention in a class diagram all we think is important and that we do not need to write down every detail UrRobot direction int 0 1 2 3 turnLeft pickBeeper Sender S Listener 1 new Listeners beeperGetted w aitForUser Fig 29 Class Diagram for Sender 2 Listeners example A suggested representation for the example with sender and listeners shows the inherited operations and attributes Attributes and operations that are not relevant for our example are omitted The attributes beep erListenerl and beeperListener2 are represented through the association and the arrow that indicates in what direction the message is sent 3 Conclusion Different sign system are crucial for the transfer of knowledge to new situations Analogies often brake and are therefore not always as ade quate as UML diagrams Microworlds have not many details but they contain all essential con cepts Therefore they are excellent examples for all different kinds of UML diagrams UML diagrams can be used for reflection and repetitions We can hope so that students learn the visualised concepts better The usage of attributes visualised messages and a sequential top to bottom
115. nclusion Review questions flash cards or mind mapping should be used regularly in a course to help acquire complex schemata by reinforcing long term mem ory 12 Analysing Code and Check with Multiple Choice Questions 12 1 An offline training on a higher cognitive level than review questions are multiple choice questions where the trainee studies code examples Examples of Such Questions The multiple choice questions used in the exams for a Sun certified pro grammer or developer may also be used in training You may find such drill question for instance in the Book of Boon 2000 The repetition or check up looks like this Firstly the trainee gets a question and a code example of up to 15 lines as prompt Then he gets a question with a set of four answers Among the answers there are always one ore two choices why the code should not compile There may also be one choice that the code does not compile for any reason An example looks like this Boon 2000 p 76 Specifying this line at the top of your source file package awt a results in a compile time error because J ava already defines an awt package b specifies that all of your classes in this file should go to into J ava s awt package c specifies that all of your classes in this file should go into your own awt package d imports all of the classes in your own awt package 58 Chapter 4 Existing solutions to overcome the problem of cognitive load
116. nd the absence of a main task method help to overcome this problem suggest to let the students play around with Roboworld the way Papert describes how children use LOGO s turtle This way students might get away from the idea of overall control even more 2 Collaboration and encapsulation Encapsulation was already demon strated in Karel because there is after instantiation no direct access to the robot s attributes Collaboration is improved by two means Firstly robots visibly exchange messages Secondly the associations between robots are maintained between to manual calls to the robots operation by attributes 3 Inheritance and polymorphism are implemented But there is no type safety missing operations will provoke a runtime error Students shall get the punishment of type unsafety so they will appreciate J ava s type safety when they will learn about it Conclusion There are solutions for this three central problems in Roboworld Most of them are not solved as well in Karel and other worlds are to complicated for beginners 83 Chapter 7 Explaining basic concepts with Roboworld The power of the microworld is its graphical user interface It lets users interact with abstract concepts in a familiar context Everything is there in the microworld so you can name the things and explain them figuratively 1 Primitive Data Types Data Input and Output and Storage 1 1 Data Beepers are the basi
117. nd to solve the spotted problem If the training concentrates on one and only one problem at a time it is an almost per fect application of cognitive load theory A little bit puzzling is the good experience reported by Bergin of the teach ing pattern Read Before Write To reveal details should cause problems according to cognitive load theory Experiences of my colleagues suggest rather the hiding of details providing classes only compiled and without access to source code Bergin rates the validity of his pattern with zero to two stars Read Before Write has a one star rating which means medium validity 7 4 Conclusion Focusing on one problem within the framework of a larger project is an excellent example of the application of the cognitive load theory It can be associated to the worked example effect Giving access to the complete source code of the project might cause lots of problems if the quality of the code is not excellent 8 Setting up a test class 8 1 What is a Test Class A test class is a class that executes automatically several tests on another class without interruption and reports any unexpected behaviour failure or run time errors There is a special free tool available to construct test classes It is called J Unit http www junit org The tester can execute as many test suites as he likes in one run The tool assembles all failures and errors in the test result The test result can be checked in case of
118. nsive usage of control structures is a clear sign of the absence of ob ject oriented programming But never ending loops may happen in object oriented programming as they occur in procedural programming Adding information about how many loops already have been executed can give the trainee a feedback about such errors 10 2 Solution In Roboworld therefore give a feedback about the number of loops that looks as follows Loop 366 enter true In the case of the sender that waits for the user to add beepers the never ending loop was made on purpose But trainees could run into such prob lems by mistake Gently giving feedback about errors does lower the cog nitive load too because the trainee does not have to keep this special error in mind when searching programming errors He perceives the error easily 11 Lower Cognitive Load by Omitting Detail Much detail need not be teached in the beginning 11 1 Variables and Operations That Are Not Essential for Object Oriented Programming Local variables class variables and class operations are not needed to un derstand object oriented programming Also other primitive types than Boolean and Integer are not essential at all 11 2 Access Modifiers Access modifiers are not needed because there is no access to attributes anyway and there is no evident demand for private methods We can ban these features from microworlds Other worlds provide more features suggest switching to J
119. nt different methods of beeperPicked We can teach that in this case both robots have the same type Listener even if they are not of class listener Arrays Arrays are not implemented As an array is nothing but a robot with a fixed number of links you can define your own arrays J ust define a new robot class and add the number of attributes you like Provide a method to preset with which of the robots in the array you work with currently Override all operations of the robot type you like to realise in this array All overridden operations just call the operation with the same name of the current robot This way you have an array just like the once used by J ava only that you do not use the special array tools but you use your own methods to provide array functionality Garbage Collection The removal of robots that one does not need any more is done by call of an operation Of course it is more work to call an operation to remove a robot than to just setting the reference to it to another robot or to null But the process of finalization and garbage collection in J ava is quite diffi cult to explain and understand Therefore preferred manual clean up in my microworld The user gets to know the problem of clean up and he experiences an understandable way to solve it Based on this experience the trainee can learn the more sophisticated method that J ava uses later easily Conclusion A big strength of microworlds is their mini
120. oals Handbook 1 Harper New York Boles D 1999 Programmieren spielend gelernt mit dem J ava Hamster Modell B G Teubner Stuttgart Also online available at http w w w is informatik uni oldenburg de dibo hamster Boone B Stanek W 2000 J ava 2 Certification Exam Guide for Pro grammers and Developers McGraw Hill New York Bishop J 1997 J ava Gently Programming Principles Explained 1 edi tion Addison Wesley Campione M Walrath K 1997 The J ava Tutorials online 2001 documentation and language specifications all available online java sun com Cooper G 1998 Research into Cognitive Load Theory and Instructional Design at UNSW University of New South Wales Australia http w ww arts unsw edu au education CLT_NET_ Aug 97 HTML 107 Bibliography Dorig R Waibel R 1995 Schweizerische Zeitschrift fur die kaufm nnische Berufsbildung 1 1995 Duval R 1995 S miosis et pens e humain Registres s miotiques et apprentissages intellectuels Peter Lang SA Bern Eckel B 1998 Thinking in J ava Prentice Hall PTR New J ersey avail able free online http w w w BruceEckel com Espich E Williams B 1967 Developing Programmed Instructional M a terial Fearon Publisher Palo Alta CA USA Fowler M Kendall S 2000 UML Distilled A Brief Guide to the Standard Object Modeling Language 2 edition Addison Wesley Gamma E Helm R J ohanson Ralph Vlissides J
121. oboter Result The instance of the robot appears on screen to the right 5 Choose the robot you wish to control in the list of robots 6 Choose the operation you like to send as message to the chosen ro bot 7 With step and run you may either stepwise or non stop run this opera tion With click on Setup Map the pane to the left changes You can now de fine a world You may add walls and beepers or re move walls and beepers You may even remove ro bots You may add walls and beepers while code is running This way you can interact with your robots See for ex ample the scenario Sender Listener 2 Listeners call the operation new Listeners first This instantiates two listeners that listen to the sender Call waitForUser Now the sender is checking permanently for beepers on the field where it stands As soon as you add beepers the sender sends the message beep erGetted to the two listeners In the scenarios above there could be several tasks for a trainee to per form e Remove all beepers in the room e Remove the beepers in the corner of the room e Remove beepers along the walls of the room 101 Appendix B Service Class for easy input output in J ava fA THIS makes it abstract Jee see sleep double sec My suggestion for a carefully commented Service class looks like this You may add other functionality like inputting and outputting to file instead of input
122. obots attributes and basic operations Afterwards we can add the symbol for inheritance and for associations as soon as we need them When we do this to summarise what we have done to solve a programming problem we reinforce the awareness for strategies we used and introduce the UML diagrams needed at the same time Interaction Diagrams Use the visual output in the scenario to draw collaboration diagrams As in a collaboration diagram we can place the symbols for the objects where we like we can draw a collaboration diagram that represents actually a one to one static picture of the dynamic interaction 4 trunLeft 6 trunLeft 15 Listener 16 Listener 3 beeper picked 5 beeper picked beeperGetted beeperGetted 7 Ya areThereBeepers 14 Sender 2 beeper true pickBeeper Fig 25 sender listener as collaboration diagram Later you may motivate the trainees to design collaborations or sequences in advance and see whether the robots meet their expectations This way the students learn collaboration diagrams easily Drawing the diagram will enhance their understanding of the interaction They can 91 2 4 Chapter 8 Supporting the Unified Modelling Language learn and train based on easy examples dynamic UML diagrams The big advantage of collaboration diagrams over sequence diagrams is that they do not visualise a program flow So collaboration diagrams emphasise ex
123. ods 7 1 Inheritance polymorphism the overwriting of methods in sub classes is regarded as the essential thing in object oriented programming Good and simple examples are therefore crucial Teaching Polymorphism With The Account Example A good example to demonstrate sub classes in action is the account ex ample For different kinds of accounts there are different rules for over drawing the account and for redrawing money from the account It is a good exercise to build together this hierarchy of accounts and to overwrite 24 Chapter 3 Key problems of teaching object oriented programming methods to implement the rules for the different kind of accounts The hierarchy of accounts should have more than one level For instance First level Account abstract Second level CurrentAccount for businesses where there are different limita tions on overdrawing according to customers credit limits No limi tations on withdrawal PrivateAccount limitations on withdrawal overdrawing is limited to the monthly income rent salary Third level SavingsAccount like PrivateAccount but overdrawing is not possible If you constrain your example to two levels students will speculate that only two levels are possible Obviously in this account example there must be an operation to check the amount of money the customer may withdraw This operation is ab stract on the first level and has different methods on the other levels
124. of thumb the more we managed to get the stu dents to program in pairs the more they learned and the less we got stu dents that did not learn at all This experience gives some support to the cognitive load theory 10 4 Conclusion Programming in pairs is an efficient way to improve teaching without any additional effort Team building causes some problems The effectiveness of this approach gives some support to cognitive load theory However other learning theories predict this effectiveness too 11 Review Questions Cognitive load theory implies to prefer offline teaching Giving sound theo retical background and working with CRC Cards and diagrams of the Uni fied Modelling Language was discussed in previous sections Using review questions is the offline technique that is used regularly 11 1 Review Questions You may find a good example for check up questions in the book of Schildt 2001 Schildt inserted a so called One Minute Drill when ever he explained three units of information that he can ask for in a one line ques tion and give a one sentence answer He repeats this check up questions at the end of each module With the One Minute Drills he avoids to over load the mind of his readers With the module check up he forces his readers to a second repetition The comments on amazon com show that these checks ups are highly estimated 11 2 Flash Cards In a live educational setting the trainer could use flash cards or mind
125. ofread this text Table of Contents Introduction Chapter 4 Existing solutions to overcome the problem of cognitive load 30 Abstract This study is centred on the design and development of a microworld learning environment for object oriented programming and object oriented design Special care was taken to meet three goals Firstly to reduce cog nitive load Secondly to maintain as much as possible similarity with the programming language J ava Thirdly to facilitate the introduction of ob ject oriented design by means of the Unified Modelling Language UML The environment can be used for visualization Support teacher s presenta tion for students training solve slightly different programming problems based on previous teaching and for the construction of new problems or solutions to problems by students The impact of cognitive load theory on instructional design is a major topic of this study Keywords Microworld Cognitive Load Theory Unified Modelling Lan guage J ava Object Oriented Programming Introduction This study has three scientific goals Firstly the analysis of the paradigm of object oriented programming and what this paradigm shift implies for teaching Secondly the analysis of the problem of cognitive load related to teaching object oriented programming and of existing methods to over come this problem Thirdly the design of a microworld that facilitates best the achievement of t
126. ognitive load theory has two explanations for the effectiveness of pro gramming in pairs Firstly because of the assistance of a second trainee the cognitive load is reduced Two trainees hold more information than one So together they are able to fill gaps in the knowledge one trainee alone would suffer There is less back and forth attention split between screen textbook and online tutorial Secondly according to the modality effect the aural explanations of the second student might expand working memory while studying the textual information on screen 10 3 Practical Problem in Education The main practical problem are the trainees themselves As nowadays every student has a PC usually it is not easy to motivate him or her to work together at one PC 56 Chapter 4 Existing solutions to overcome the problem of cognitive load Several precautions help to overcome this problem e Make teams where a better student works together with a weaker learner e But do not make the difference too big Do not assign the best trainee to the weakest e Instruct them to use one PC for browsing manuals and the other for programming e In case of non native English speaking students one of the trainees should know English well This reduces the cognitive load added by the English language Experiences at our institution for adult education When we managed to motivate students to program in pairs we found it very efficient As a rule
127. ogramming One problem is to design a house by placing beepers Variations are plac ing beepers to form digital digits or placing beepers around walls The other problem is to harvest a field of beepers To show the advantages of a good design the problem is alternated Robots should draw different type of houses by plac i ing beepers or the size of the beeper field is O Taig ae changed Fig 12 drawing with beeners Both problems can be done in several ways 1 One Robot one class several methods 2 One Robot several classes 3 robot teams One Robot One Class Strategy One robot in one operation could do the entire job Bergin lets the stu dents first do the whole harvest task in one method Afterwards the job is analysed Repetitive sections are separated and de fined in methods With this predefined methods one robot does the job by executing a main method that calls sub methods For alternations a set of different basic method should be set up The smaller and easier to read the basic methods are the less different methods are needed the better the solution is This is the procedural programming approach One Robot Different Classes Strategy Variations in robots behaviour can be made by subclasses In the harvest example different types of harvester could have all their own method to harvest a row Some robot classes harvest a long row some a Short row Only this method is different from one harvester to
128. oks that help once the basics are under stood 9 3 Conclusion User interfaces are an interesting field for studies once the trainee has learned basic design patterns and concepts 10 Chapter Summary Compared to procedural programming object oriented programming causes not only different problems It causes also much more problems in the very beginning of a course J ava adds even more problems by its complicated graphical user interface and its poor support of a code line user interface 29 Chapter 4 Existing solutions to Overcome the problemof cognitive load There are several ways to work around the problem of cognitive load when teaching J ava You can ignore object oriented concepts when teach ing J ava in the beginning Give a sound theoretical background first Start with software design with the Unified Modelling Language Start with sin gle classes and test them against test cases the teacher provides The usage of microworlds is compared to such alternate possibilities 1 Ignoring Object Oriented Concepts When Teaching the Language Java 1 1 1 2 There are three big pros for this approach the common basis of proce dural programming and object oriented programming is the one the avail ability of tested training material the other the possibility to do interesting projects in J ava without object oriented programming the third Common basis of procedural programming and object oriented programmin
129. om even says We learned J ava gently not J ava But it cannot be the fault of the approach K N King 2000 who gets for his book an amazing suite of ten enthusiastic five star ratings uses exactly this approach Avoiding the graphical user interface and us ing a class to ease input from keyboard and output to screen One reader writes All J ava beginner books skip the input function in J ava applica tions You spend half your time wondering how you input anything into a J ava program Mr King solves the problem by writing a Simple Input class that you import like any other class and makes J ava application input sim ple and fun This increases your interest in J ava and makes it more fun to learn You can actually write useful J ava programs from page sixty three King comments his three classes in appendix E King 2000 p 759 He restricts himself to three classes because as he writes I m not a big fan of instructor supplied classes so I ve kept the use of these classes to a bare minimum Besides writing an input class and importing it it is also possible to write a class that provides basic services and subclass this class An example of such a class can be found in As written in the section Read Before Write versus Hiding Details p strongly recommend either to design and comment this Service class well or to hide the content of the class J oseph Bergin suggests in his teaching pattern for object oriented programmin
130. on The combination of spo ken text and graphics would be such a presentation Effects under investigation are according to Cooper 1998 1 the pro cedural learning effect 2 the imagination effect 3 the colour coding effect and 4 the interaction effect Chapter 1 Cognitive load in a J ava short course 2 3 What It Is Not The cognitive load theory is not a global learning theory It is not meant to explain theoretically all learning experience It is meant as a tool to im prove teaching and the design of educational material Compared to the three classical learning theories there is for me a big difference The classical theories behaviourism cognitivism constructivism all try to explain what enables learning They explain what to do Cognitive load theory explains why learning is hindered It explains what to avoid It does not explain how a schema is learned It explains only why learning does not take place Therefore it seems to me complementary to existing learn ing theories To visualise that fact with an analogy you can improve the overall per formance of a racing car by tuning the motor that is what classical learn ing theories do Or you can improve it by reducing weight and improving aerodynamics this is what cognitive load theory does Usually we think of the first and forget the later and as with racing cars we would gain more with the latter 3 Cognitive Load Theory and Instructional Design
131. on the impor emphasis on important tant information information e items are out of order e items are in a logical e important items are not order marked up e straight forward e several items must be method to solve the considered simultane problem can be ap ously because there are plied several steps to the goal e oral and visual infor mation that go to gether well 0 97 2 2 2 3 Chapter 9 Overall conclusion The thesis is The heavier the cognitive load rated this way is the more students will fail to learn found quite often that could relate problems experienced during teach ing to cognitive load And that instructional material that was experienced as being efficient often had elements of lower cognitive load Some times could relay not only on my experience but also on experience of other teachers or students For instance on readers ratings of books on amazon com Based on this evaluation would say that the cognitive load theory is a valuable tool to analyse instructional material It might_be used to choose the material to consider and what to put away See Chapter 1 Cognitive bad in a ava short course Harting at page 3 and Chapter 4 Existing _ starting at page Improving Instructional Material checked Roboworld which basic idea was to have a more J ava oriented simpler version of Karel for cognitive load found different things that needs to
132. onstructivism are like the engine that powers our car but the cognitive load theory is like weight and aerodynamics that Slow down our racing car Often we do not have the time and the money to prove that replacing some material by lighter material or making a smoother shape really does make our car faster Nevertheless it is impor tant to think about such improvements permanently We might get sur prised sometimes The whole system might not react as predicted For instance we might loose traction when we remove some weight at the wrong place So it is with cognitive load For instance Sweller 1990 p 178 reports of worked examples without positive worked examples effect in geome try The inefficiency of the worked example effect in this examples as he 60 13 3 Chapter 4 Existing solutions to overcome the problem of cognitive load could prove in this later study Sweller 1990 was according to the split attention effect Counting or Rating Sweller 1988 p 272 is counting the cognitive load for a mathematic task based on the number of 1 statements 2 productions 3 cycles to solution 4 conditions Because of the heavy cognitive load could not quite follow his calculations Anyway most of the time in practice would suggest to rate the amount of cognitive load As teacher we can make some estimation what our students know when they start a course we can also figure out whether the amount of new or inte
133. onstructor ur_Robot street int avenue int direction beepers int query frontlsGlear boolean nextToABeeper boolean nextToARobot boolean facingNorth boolean facingSouth boolean facingEast boolean facingWest boolean anyBeepersInBeeperBag boolean Fig 11 the Application Programming Interface API of Karel and the Ham ster Model 7 The user can experiment with the microworld and learn there the basic know ledge of object oriented programming will discuss this in this study on the following pages Teaching Polymorphism with the Microworld Karel Bergin 1997 shows in chapter 3 6 p 35 how to override inherited opera tions with different methods and how to call the inherited method to use it within the new defined method s body In chapter 6 7 Bergin 1997 p 166 170 shows how to use one pointer to a Robot to address Robots with different behaviour However the ex ample Bergin uses is not convincing Unlike for instance the Account ex ample it misses to demonstrate an obvious advantage of polymorphism 53 9 4 9 5 9 6 Chapter 4 Existing solutions to overcome the problem of cognitive load Teaching Collaboration with The Microworld of Karel Bergin only devotes a small chapter Begin 1997 3 11 Robot teams p 55 58 to the topic of collaboration He demonstrates with this small chapter that you can introduce key concepts of object oriented program ming r
134. or the novice But the novice would like to do real things This means he or she would like to write small applications that have a graphical user interface and code that he or she understands com pletely 4 6 Command Line Interface Even the set up of a command line interface with J ava is very demanding Comparable to the graphical user interface the command line interface uses advanced features of J ava 5 Conclusion In a typical J ava short course there is a high level of intrinsic cognitive load Special care has to be taken to reduce cognitive load added by course design and course material Therefore we should take advantage of any means of reducing cognitive load 10 Chapter 2 Paradigmshift to object oriented programming Procedural programming and object oriented programming are based on different problem solving strategies and have different key concepts This has a heavy impact on education 1 Motivation for Object Oriented Programming Object oriented programming was created because of shortcomings of procedural programming Procedural programming processes data input and produces data output Whenever the structure of the processed data changes large parts of the application need revision This happens often for instance if the user likes to have a field for an e mail address in his address book In such cases procedural programs are difficult to maintain In object oriented programming however the addres
135. ore Technical Explanation Therefore explain my students that objects have sequential numbers Usually these numbers are hidden The variable that holds a reference holds the object s number The only way to call up an object s attribute or operation is by this number When explaining objects often use these pseudo serial numbers instead of objects name For instance in a object diagram instead of showing an object like myObect ClassName CassName or show it like 00462 Cass Name If learners understand the concept of assignment they do understand the concept of assigning a serial number to a variable The only additional in formation to learn is the fact that serial numbers cannot be used directly in program code like 00462 toString But you can use it directly for further programming without assigning the serial number to a variable You take the serial number returned from an Operation and use it as a reference to the object new Integer 205 toString This is understandable as soon as you imagine that new Integer 205 returns a serial number of the new object Conclusion Objects references are very important Visualising the reference number of objects can support this acquisition 18 Chapter 3 Key problems of teaching object oriented programming 3 Understanding Argument Passing with Messages 3 1 3 2 3 3 3 4 Description of th
136. ot ob solete It is quite efficient as long as there is a large and stable demand 33 2 7 2 8 2 9 2 10 Chapter 4 Existing solutions to overcome the problem of cognitive load like in the production of cars or in banking transactions It is rather incon venient when customers demand and the knowledge in the field is chang ing permanently Metaphors and Microw orlds Bergin mentions that metaphors brake at some point He writes Bergin 2000 Metaphor is important since it helps you with a framework for thinking about something unfamiliar Every metaphor breaks down at some point however You may think of the robots in the microworlds of J oseph Bergin as ob jects will discuss this metaphor more deeply later in the text see Chapter 7 Explaining basic concepts with Roboworld at page 841 per sonally believe that the robot object beeper primitive data microworld external storage metaphor will brake at almost no point Plus the trainee works in the metaphoric situation There adaptation can take place Only there still is some transfer to teach when moving from a microworld to real programming But this transfer is a feasible step not a jump over the ocean Books That Do Not Use Metaphors and Explain Objects Directly Eckel 1998 p 27 online 2001 chapter 1 refers to Alan Kay and ex plains an object directly as Think of an object as a fancy variable it stores data but you can also ask it
137. otal Immersion Read Before Write works fine According to my experience the quality is based on Consistent naming and coding Code comments where needed The context is evident for instance the responsibility and the col laboration of the class are explained The code is concise but avoids abbreviations that execute two steps in a single command For instance it should rather reed i while i lt max than while i lt max Methods are not too large The J ava Tutorial of Sun Microsystems contains a good example of useful code as stated above A lot of material is not good enough for Read Before Write Therefore you would better not give access to the source code of this part of the pro ject Otherwise trainees loose lots of time studying code that does not 48 Chapter 4 Existing solutions to overcome the problem of cognitive load have the quality to be used for Read Before Write This might be very inef ficient Plus it gives trainees a bad model on how to write code 7 3 Support for Cognitive Load Theory Evidently giving the trainees a single problem within a larger project he or she can focus on specific problems and the schemata that may be applied to them They do not only learn the schema to solve the problem but also to recognize the schema within a real live scenario Both things do not involve unnecessary redundancy The first schema is to scan for the spe cific problem the seco
138. ou should probably rethink your strategy However statics are pragmatic and there are times when you genuinely need them so whether or not they are proper OOP should be left to the theoreticians Indeed even Smalltalk has the equivalent in its class methods To sum it up static objects provide a service like any other object They are available all the time throughout execution of the program Instances of the Class The second kind is the regular objects the instances From this kind of object there can be no instance then it is a utility class like class Math there can be one and only one instance then it is a singleton or there could by many instances The latter is the usual case To use the concepts of object oriented programming correctly we can use object as super category of instance and static object Therefore it might help learners when we draw object diagrams with the static object and the instances of the class This is not foreseen in the Object Management Group s 2000 Unified Modeling Language Specification version 1 3 But it might help to avoid a lot of confusion between classes and objects The Object Management Group suggests mixing classes and objects in static diagram This might be convenient to experts it is confusing to novices Shared Name Space of Instances and the Static Objects of its Type In the code inside a class you can refer to the attributes and operations of all the static obj
139. output in Roboworld supports the learning of UML diagrams better than existing worlds do 95 Chapter 9 Overall conclusion Is there evidence for the effectiveness of Roboworld and what can we learn from the analysis in this thesis and from the design of Roboworld about cognitive load theory Missing tests but some evidence for usefulness of Roboworld There is a major flaw of this Master thesis did not have the time to test Roboworld in classroom yet But am quite confident for two reasons 1 1 There Is Only Good Feedback about Karel Used in Classroom Karel the robot is used at several institutions for higher education found nowhere any negative feedback about using Karel in classroom Larry Burks a teacher from Harvard University Graduate School of Design writes about Karel was looking for a way to introduce my students to object oriented programming without scaring them out of the class in the first 10 minutes Karel the Robot is a powerful aid to teach ing because it has a very limited vocabulary which is easily ex tensible and encourages students to build their own compo nents quickly It is a great way to introduce concepts that will be directly analogous in C and J ava Cathy LeBlanc Assistant Professor of Computer Science Plymouth State Plymouth NH uses microworlds also as project idea in her courses She wrote about Karel We ve used Karel the robot and have ha
140. pproach We tried this approach in our institution for adult education It is not a bad approach We needed one week 30 lessons to do it CRC Cards and statechart diagrams are most useful when you follow this track With UML and especially with CRC Cards one can involve learners in ac tivities Good Activities for Working with CRC Cards and UML Reading comprehension of diagrams e Explaining what you see in a diagram in your own words e Given a diagram and different statements trainees decide which statements are true and which are wrong Drawing diagrams e Given some statements in natural language trainees design diagrams e Given a class diagram trainees draw object diagrams that are compati ble to the class diagram or vice versa This is very important to under stand the difference between objects and classes e Given a sequence or collaboration diagram trainees draw class dia grams that contain as operations the messages sent between objects Playing objects involved in the program flow Given is a task to complete and the objects or classes that collaborate with each other The trainees have to find a program flow for the collabo ration The rules you give for this exercise 1 You communicate only with messages A message contains the addressee a command and additional in formation 2 The addressee takes over complete control and keeps it until he gives it back to the sender of the message 3 The addressee may ca
141. proach you may reinforce this behaviour Also learners are bewildered by this entire un necessary object oriented overhead around the operation main J oseph Bergin 2000b in his online pamphlet Why Procedural is the Wrong First Paradigm if OOP is the Goal mentions several reasons why this approach should be wrong He mentions that developers used to pro cedural programming need one or more years to grasp the paradigm of object oriented programming He also mentions the different strategies to design structured programs and object oriented programs Conclusion In fact strategies for procedural programming and object oriented pro gramming are different as discussed in Problem Solving Strategies Com pared Jpage 1 But why not teaching the basics of J ava programming as procedural programming like Dietrich Boles 1999 does during the first months of education before making the move from procedures to methods from overall control to client server thinking Procedural pro gramming first promoted from Gibbons 1998 for instance might not be absolutely the best way but it might be the best way under circum stances that are not unlikely would therefore suggest this approach only if you meet two prerequisites 1 You can really relay on good and tested material on procedural pro gramming but not on object oriented programming 2 You have enough time to do the second step from procedural pro gramming to o
142. ral programming language and later to J ava Boles uses J ava to introduce procedural programming concepts only The planed extension to show object oriented programming was postponed to 2003 62 Chapter 5 Existing microworlds for teaching J ava The idea behind LOGO is stated in Papert 1980 The enthusiastic expec tation of Papert to have LOGO as a touchable and loveable math world which would allow all children to enter his fascinating world of mathemat ics were not met Mendelsohn 1990 Or may be do we not know about their long term effect But at least Papert showed us that pro gramming can be a children s play However LOGO is not just a toy it is an even more powerful language as the procedural programming lan guages such as BASIC of those days The idea of the loveable and touch able has been maintained in Karel and especially in the Hamster World But it is used not for children it is used for students 1 3 WYSIWHa instead of WYSIWiG Rajan 1990 refers to J ones 1984 p 777 and reports that special problems are related to the flow of control Missing know ledge about flow of control hinders students from writing programs and understanding pro grams Rajan 1990 p 391 therefore wants for programmers WYSIWHa What you see is what happens in analogy to the WYSIWiG What you see is what you get of end user applications A microworld offers exactly this WY SIWHa All what happens happens in t
143. ramming harder to teach than procedural programming In this chapter we take a closer look at these key problems They are variables pointers object refer ences in J ava static attributes and operations and last but not least the collaboration of objects 1 Understanding Variables in Java 1 1 1 2 1 3 Experienced Problem As most people nowadays work with spreadsheet application like 1 2 3 or Excel you would not expect that people have difficulties with the concept of variables Therefore underestimated the difficulty to make the transfer from a spreadsheet cell to the concept of a variable in J ava Analysis of the Problem In a spreadsheet application a cell address like B4 is rather an instruction to look up information in another cell but a variable This is evident with relative addresses where you look up the value in a given distance As this addressing is most common users might have a notion of cells as a look up instruction rather than a variable Absolute addressing is only some Special case of a relative look up Most learners as long as they are not mathematicians are unfamiliar with variables Variables are therefore something unfamiliar More Cognitive Load Related to Variables in Object Oriented Programming than in Procedural Programming But why do variables cause almost no problems in procedural program ming but can become a burden in object oriented programming In procedural programmin
144. rams is different We will discuss this in the next chapter In J ava the argument passing by value is a very important topic It is well worth to invest several lessons to provide trainees with enough experi ence In several books String and StringBuffers are used to explain value passing in J ava As Strings are immutable they cannot be used for output or input output arguments StringBuffers are mutable and can be used for it Conclusion Messages and argument passing are a very demanding task with a heavy cognitive load It is interrelated to other topics with high cognitive load like variables and object references Approaches that do not overload the learners working memory are crucial 4 Grasping the Idea of Object Oriented Programming 4 1 The most challenging part in teaching object oriented programming is get ting the students to understand the idea or paradigm of object oriented programming Main Problems in Teaching the Paradigm of Object Oriented Programming Let us assume the trainee knows procedural programming or we taught the parts of object oriented programming that are congruent to procedural programming first Now what impedes trainees to work according to the paradigm of object oriented programming I experienced that three prob lems are most cumbersome in practise 1 Falling back into the paradigm of procedural programming s overall control and therefore abusing static attributes and static methods 2
145. rch about the readability of German text They found four criteria factors for readability and con structed a short course to learn to check for this four factors and improve the readability Schulz von Thun e a 1974 then checked whether this training was efficient Well of course it was The most remarkable to me 3 3 3 4 Chapter 1 Cognitive load in a J ava short course of this check up are two things Firstly a short training that only helped trainees to check for the four factors already caused a significant im provement readability raised about 50 Secondly in the control group that studied a style guide readability even dropped insignificantly This did not happen because the style guide suggested tips that where not con gruent with the four factors It happened because the trainees had to consider to many rules at the same time By the way the four factors coincide with cognitive load theory The first factor is simplicity length of sentences known and figurative words That means each sentence causes no extra cognitive load by unknown words or to many words in a sentence The second is text organization logical flow introduction to paragraph mark ups of important words titles That means no extra cognitive load needed to bring the ideas ex pressed in the text into a logical order The third was length of the text The text should be as concise as possible But shortage should not get in the way of simplic
146. refer ences should become all natural for students The will be taught that a field instance variable of a robot holds that reference number This num ber may be used for UML diagrams as well instead of variable names to Support this concept even more Conclusion Object reference should become easier to learn by making them visible Understanding Argument Passing with Messages At the moment only passing a Boolean variable as return value is imple mented The implementation of passing one argument forth a back of any type will be added Parameter passing happens visibly with drawn messages between robots Already the visible exchange of messages will help to understand argu ment passing better Student get an impression of request and answer between client and server Conclusion For me this is a important feature of Roboworld It has first priority when extending the features of the existing version Grasping the Idea of Object Orientated Programming stated and motivated that three things are important to grasp the idea of object oriented programming 1 Not falling back into the paradigm of procedural programming s overall control and therefore abusing static attributes and static methods 2 Collaboration and encapsulation 82 Chapter 6 Reducing cognitive load in Roboworld 3 Inheritance and Polymorphism 1 Overcoming overall control The instantiation tool the possibility to trigger any operation manually a
147. resting things This way he or she can directly experience what a class does and what it is for The keywords are limited to class extends and void at the beginning Besides this key words the user learns how a simple class head and body looks like how a simple method head and body looks like and how a call to a basic opera tion looks like He or she can soon call from one of his operations a self defined operation Thanks to the template method there is now need to learn anything by hard Everything is obvious concrete and understand able What a difference to the hello world application that shows odd things such as static methods access modifiers array definitions and with System out printin a reference to the standard output stream via a Static variable of the predefined class System implemented an all in one window solution The usage of multiple win dows as in the Hamster Model or in Karel splits attention unnecessar ily Of course further improvements are possible for instance the Hamster Model uses colour coding for keywords methods and classes a pop up menu for keywords would be an idea that could implement easily 78 Chapter 6 Reducing cognitive load in Roboworld To conclude Already the existing microworlds omitted a lot of cognitive load Implementing a learn mode and a all in one window solution could diminish the cognitive load even more 8 Call a Overridden Methods in the Super Clas
148. retical discussions about specifications and testing Experiences with this Approach used an example that was too difficult Direction The class Direction should store a value between 0 and 27 to indicate a direction Besides static operations like the conversion of degree formats it provided opera tions like turnLeft double degrees and turnRight double degrees The mathematical complexity discouraged the trainees and distracted them from learning J ava But would do it again with a more suitable class such as Temperature or Fraction Avoid Mathematics in Examples Trainees outside technical universities usually have no mathematical know ledge Even trainees with a fair mathematical background do not like to integrate mathematics in programming There is no need for extended mathematics anyway J oseph Bergin and other authors and trainers show that instead of using the utility class Math and mathematical operations one can operate on String and StringBuffer Integer operations as in Frac tion that students usually learn in their sixth school year seem to be al right Cognitive Load Theory and Test Classes According to cognitive load theory writing classes against a test class should be even better than fixing one problem within a large framework The trainee starts a class from scratch Therefore there is no redundancy Conclusion This approach is an interesting alternative to fixing one problem within
149. rogrammed operations to complete a one and only major task should be the exception not the rule A one and only main task supports procedural thinking and this is just what we want to avoid The Possibility to Trigger any Operation Reduces Cognitive Load Procedural thinking means to do your planning from the whole the top to the details the bottom This exactly produces a lot of cognitive load for the same reason as the goal free effect does The novice should look for solutions bottom up finding methods that do some of the job experiment ing with them testing them and improving them It is crucial that he can call up all this methods manually Also this bottom up idea reflects the idea of Papert 1980 Children or students should experiment Build up their knowledge and experience driven from their own desire Playing around affects students and children much more than solving a problem Solution Part Three The Macro Like Leam Mode Fig 18 robot control centre with leam mode 72 4 6 4 7 Chapter 6 Reducing cognitive load in Roboworld To help students even more added a macro like learn mode In this mode every method that has been called up will be written into the code of the class that is currently open for editing Why Instantiating a Robot Manually Firstly instantiating manually let you avoid the new statement in the be ginning The user can experiment with robots without knowing how to set
150. rol back it may be the passing of the return value This return value may be used directly or it may be assigned to a vari able All this single steps should be visualised 5 4 Giving More Comprehensive Feedback about the Sequential Execution There is even more need for information about the sequential execution process 76 5 5 5 6 Chapter 6 Reducing cognitive load in Roboworld Fig 23 Sequential feedback about execution This feedback is given in the panel at the bottom right The user can com pare execution of the method and the definition of the method in its class Well to have three panels showing three sights of the same one sight as class definition one as sequential execution and one as robots in actions are not accurate according to redundancy effect This might be a field for further improvements For instance consider displaying the sequential execution as a pop up text when clicking on a method or on a robot Acknowledgement This idea is based on J oseph Bergins Objects in Action Bergin 2000 b Bergin writes lt is useful to think of an executing object oriented program as a graph or web of objects nodes and communication paths arcs An object communicates with another by sending it a message This message is a request for service The sender is the client and the receiver is the server The receiver will fulfil the service request and perhaps return information to the sender Often t
151. rrelated informa tion is high With some empathy we can also rate how much cognitive load our instructional design adds to the learning situation As Langer e a 1974 point it out often rating is much more accurate than counting The number of words in a sentence does not imply that this sentence is difficult to read For instance you can replace to get around by circumvent and save two words but the sentence gets rather more complicated than simpler Therefore rating the cognitive load is an accurate mean in practice If there are time and money however it would always be nice to check by testing whether our expectation are met Most often this is not possible to do and most often we will not fail with our rating neither 61 Chapter 5 Existing microworlds for teaching Java This chapter mentions the initial ideas behind microworlds gives a short history about learning to program with microworlds and evaluates the existing microworlds 1 Motivation for Microworlds in the Field of Programming 1 1 A Look at the Preface of the Existing Worlds The initial idea of microworlds is to provide students a familiar environ mental They should not be forced to think in bits and bytes numbers and characters There is already a large amount of new information new con cepts and new procedures to learn The danger to loose sight of the es sential in programming that is problem solving is high Students get lo
152. s This is crucial in the microworld Otherwise it is not possible to show that different types of objects may move differently for instance Inheritance according to my experience does not provoke a heavy cognitive load any way As overriding methods is already absolutely convincing in Karel al most no improvements must be made only made a minor improvement because other than Karel Roboworld does not display the executed code segment Therefore set information about the type of robot a method belongs to into the sequen tial feedback For instance the feedback line could look like this gt Listener 15 c 3 r 4 dir 2 carries 0 turnLeft as UrRobot Listener 15 is the class and the serial number of the robot c 3 64 dir 2 carries 0 is the state of the robot turnLeft as UrRobot not only tells the method but also in which class the method is defined turnLeft in this case is inherited from class Ur Robot To conclude generally there is no evident need to reduce cognitive load while teaching this topic But displaying the class that a method belongs to at runtime might reduce the cognitive load in complex situations 9 Control Statements If While Loop 9 1 9 2 Here two questions arise firstly what features shall we support and sec ondly how shall we deal with a fixed number of repetitions loops Existing Worlds There are two solutions Karel that only supports if
153. s book and all opera tions on the address book are built into a small module a class Adding a field means only modifying the methods in this class Of course the view and control of the class needs also modifications But all other parts of an application that do any transaction with the data defined in this class will never be affected Also as the class defines data and methods to modify this data in one file this class might be used for other applications as well Transferring parts of data structures and related procedures out of a procedural pro grammed application is much more difficult 2 Problem Solving Strategies Compared 2 1 Procedural programming and object oriented programming uses two com pletely different problem solving strategies This implies other key con cepts Focusing on the concepts of object oriented programming may re duce cognitive load Procedural Programming Starting point of procedural programming is a main task of data procession that should be performed For instance a banking transaction like buying shares This main task is divided into subtasks For instance checking clients credit limit checking price limits getting actual stock market price accept offer or send an offer to stock market put shares into clients de posit withdraw money from clients account Again these subtasks are divided into smaller tasks until the tasks meet two criteria Firstly the programmer does not have to rewrite
154. s to take an real simple project and ask the trainees to solve one single problem within this project The second is to write unit tests first and ask the trainees do define classes or part of classes that comply with these tests The third and most interesting are microworlds where you ack the trainee solve proven in the micr 7 Trainees Solve a Single Problem within a Project 7 1 Key Idea In object oriented programming responsibilities are shared Therefore your students may work on a small part from a larger project J oseph Bergin calls a predefined application or framework as basis for learning an arte fact He calls the technique of fixing minor flaws in this artefact a Fixer Upper He mentions several ideas of how to use it You can implement these ideas simultaneously sometimes Bergin 2001 lists and describes When the artefact is introduced at the beginning of the course and introduces the key ideas of the course then it is also an Early Bird When the artefact is very large then it is also an instance of Larger Than Life If the artefact is also illustrative of some important topic then it is also an instance of Toy Box 47 7 2 Chapter 4 Existing solutions to overcome the problem of cognitive load When the artefact illustrates the overall topic of interest in the course it demonstrates Lay of the Land If the repaired artefact is useful in some larger context it can also be a Tool Box instance T
155. se fragments do not cover a topic in detail as a reference book does 2 Problem solving should be possible with these fragments Microworlds as discussed in this thesis are a typical example for a spiral approach But one can find other excellent examples 37 4 2 Chapter 4 Existing solutions to overcome the problem of cognitive load Kim N Kings Spiral Approach An excellent example of the application of the Spiral Approach for teach ing J ava can be found in King 2000 King motivates his approach King 2000 p xvili as follows l ve employed a Spiral approach to many topics gradually adding detail over the course of several chapters rather than covering each topic in a single place The treatment of objects and classes is spread over Chapters 3 7 10 and 11 for ex ample Control structures are covered in Chapters 4 5 and 8 In fact in his curriculum he often turns back to important topics see on next two pages TAble 3 38 Chapter 4 Existing solutions to overcome the problem of cognitive load Difficult topics of object oriented programming Common topics for structured and object oriented programmin Topics of object oriented programming Chapters in King s Method call and Objects and object Inheritance and Objects Collabora textbook Variables return references polymorphism tion 1 Getting Started 2 Writing J ava 2 4 Using Vari 2 9 Methods Programs ables 2 5Typ
156. ss experienced than others You have Forces You want to ae more done than your most productive person can do You want your less experienced people to learn from your more experienced people You want to structure your organization to avoid needing n squared communica tions channels Therefore Pair up your people When applicable each pair should have a relatively experienced and a relatively inexperi enced person For work being done at a computer put the rela tively inexperienced person at the keyboard so everything the experienced person says has to flow through the novice to the computer The point is not for the guru to dictate to the green horn on the contrary putting the novice at the keyboard is meant to keep him or her more in the loop When as happens occasionally that doesn t provide enough bandwidth the ex perienced person will say Let me drive that s not a prescrip tion that s what s frequently said and will show something instead of teaching it at a more leisurely pace When one member of the pair is not following what s going on he or she can ask to drive 10 2 Impact of Programming in Pairs Collaborative Learning is studied well and shows in general a positive ef fect A negative effect of collaborative learning is the fact that low achievers progressively become passive Dillenbourg 1996 p 8 11 Therefore it is a good idea that the less experienced should drive sit at the keyboard C
157. st in syntactical and technical detail Boles 1999 page 3 adds to his initial thoughts very figuratively Der Kampf mit dem Compiler bekommt somit h here Priorit t als der Programmentwurf an sich und kann fr hzeitig zur Frustration f hren Translation The fight against the compiler gets higher priority than program design and soon may lead to frustration Bergin 1997 p vil writes in his preface similarly However the concepts of Karel are still as vibrant and valid an introduction to the programming and problem solving processes as they were when first introduced Here the objects are robots that exist in a simple world There can be one or several robots assigned to a task The programming task is divided into two parts The first part is defining the capabilities of the ro bots that are needed The second is providing a description of the task for the robots to perform The programmer uses his or her problem solving skills on both parts of this task 1 2 Short History of Microw orlds Karel the robot was created in 1981 to teach Pascal Bergin 1997 p vii it was adapted to C by Bergin in 1997 Bergin adapted it to J ava too but did not officially publish it but a version can be found on the web Bergin 2001a Boles refers to two roots for the Hamster Model The microworlds based on LOGO Ross 1983 and Karel the robot The later was first adapted to ELAN Oppor 1983 Klingen 1983 and 1985 a procedu
158. t while mountain still goes up is also a good example for usage of the while statement 66 3 4 3 5 3 6 Chapter 5 Existing microworlds for teaching J ava For Statement Instead of the For statement with its complicated syntax Bergin 1997 p 101 103 uses the Loop statement Boles 1999 avoids looping at all Recursion Bergin and Boles both discuss recursion with good examples As recursion does not occur in object oriented programming regard this examples as obsolete do not recommend using them in a course about object oriented programming Conclusion As Bergin 1997 shows us important concepts of object oriented pro gramming and object oriented design can be teached efficiently with mi croworlds With some improvements in the choice of exercises we could do even better 4 Disadvantages of Existing Worlds 4 1 4 2 4 3 There are some disadvantages of the existing worlds Disadvantage of The Hamster Model The Hamster World is not object oriented As problem solving is rather different in procedural programming and the main idea of microworlds is teaching problem solving methods the Hamster World is not suited for a short course in object oriented programming The advantage of the Hamster World is its nice interface and the usage of pure J ava code Karel This is probably the best tool for a first contact with object oriented pro gramming The code is more C like as J ava like
159. t oriented programming it is needed pretty early Problem Description If you do not enter technical aspects only interesting for expert program mers pointer and object references are the same In fact a pointer in the procedural programming language Pascal has more similarity with a J ava object reference than with a pointer in the procedural language C From the conceptual point of view pointer and object references use the same schema they apply to the same problems Pointers are difficult because 17 2 2 2 3 2 4 Chapter 3 Key problems of teaching object oriented programming naming a place where information is stored a variable is more natural than naming the reference to that name a pointer Learners may even be familiar with the concept of variables from mathematics But there is noth ing like pointers in the real world Metaphors for Pointers To explain pointers teachers created metaphoric explanations The meta phor that a pointer is like the address of a house where different people may live at different times is widely used At address nr 14 there might live family Miller They move out and Brown moves in So nr 14 may point to Miller at one time Brown at another time This metaphor works fine in procedural programming am not very enthusiastic about such metaphors They build extra item to be remembered As long as metaphors are still needed to scaffold the concept they use up working memory M
160. t to decide in which order defining a class method call and return value and last but not least instantiation should be taught Deviation Short Explanation of Use Case Diagrams Use case diagrams are part of the Unified Modelling Language UML A use Case diagram as fig 1 on the next page usually shows all pos sibilities how to use an application For me it is also a way to outline a curriculum Every use case describes an activity Arrows show the in terdependencies of these activities Base activities should be learned firstly because other activities extend the material of a first activity Important the arrow points to what needs to be learned firstly the basic activity Outlining a use case diagram one may split up larger activities into smaller activities as long as there is still an activity that the trainee can carry out By the way the presentation of the material as use cases diagrams may facilitate the learning of use case diagrams It may also help to give an overall view of the course and feedback on the ground the learners have covered while proceeding in the course Chapter 1 Cognitive load in a J ava short course Call static Operations fromthe AP write a simple class ore Information in a Variables includes includes includes 7 P write a simple i progranm includes use control basics object or structures A includes write a simple jav
161. the overall withdraw limit of any objects of type creditable you wish Conclusion There are some evident examples to introduce polymorphism and inheri tance Polymorphism is a complicated and abstract topic However it is not as difficult to teach as collaboration User Interface Related Problems 8 1 8 2 8 3 8 4 Because of its richness a graphical user interface is difficult to implement Books and courses avoid it but DOS and Unix like code line interfaces also problematic Description of the Problem Graphical user interfaces GUI are very complicated Setting up a user interface with swing is very well documented in the J ava tutorial Never theless because of its richness and complexity it is difficult to under stand for the novice But the novice would like to do real things This means he or she would like to write small applications that have a graphi cal user interface and a code that they understand completely How can we scope with this wishes and circumstances Need for Visual Feedback Confusion between Objects and Related Views and Controls on Screen One goal of graphical user interfaces is to give the user feedback The user will get feedback not the programmer For the novice programmer the graphical user interface GUI is a burden Because in a graphical user interface the visual representation should be separated from data There fore there is a multi step process to transform the settings in
162. the same code twice Secondly the task is small enough to be written to code with no further analysis This means the typical problem solving strategy of procedural program ming is a recursive task A procedure WRITE_PROGRAM looks like this 11 2 2 Chapter 2 Paradigm shift to object oriented programming IF Task is small enough and not redundant THEN write the Procedure for it ELSE do WRITE_PROGRAM Besides this top down strategy there is also a bottom up strategy It says implement elements that are relevant for the main task Chain together the elements to build the solution In practice a mixed strategy is used Object Oriented Programming In object oriented programming we build a model of the reality the prob lem domain of our application If we do it with class diagrams this model looks much the same as an entity relationship model used for database design This means the starting point of the developer is data not proce dure The developer treats every element of this data structure as one small application This small application may act as a server application and as a client application at the same time That means the application can be called to provide a service for instance provide the credit limit of a cus tomer and calls other servers to provide services to them for instance asks for the customers monthly salary to set the credit limit gt gt 1 getCreditLimit 2 getCreditLimit
163. thods are acquired with one class no splitted attention courses usually start with existing classes of the Application Programming Environment API This can be done also without attention split when the used existing classes of the API and their usage are explained first After that one starts with two classes and their objects exchanging messages Solution Step by Step or Spiral Approach Training that goes smoothly from the call of simple methods to more so phisticated method invocation do lower the cognitive load You may start with simple methods firstly and post pone sophisticated method invoca tion to later in the course Spiral Approach References or Pointers as Arguments and Return Type References as arguments and return type do not cause problems only in object oriented programming but also in procedural programming Firstly references are like pointers to records We discussed this topic already earlier Secondly references in J ava are the only way to have out put arguments and input output arguments That means arguments do not only provide additional information to be processed within a method but can also receive information during the execution of the method In proce 19 3 5 Chapter 3 Key problems of teaching object oriented programming dural programming developers take care not to alter other variables than the out and in out arguments to avoid side effects The structure of object oriented prog
164. ts If these concepts were not un derstood learning is hindered by redundancy Redundancy might be one reason for the weakness of this approach The main problem as it seems to me lies somewhere else There is a high risk that trainees stay inactive just read theories and do not try to apply their own knowledge to new situations Or that their activities remain on a low level typing and copying code trying to fix code without exactly knowing what is going on receiving solutions from teacher and peers rather than fixing code themselves 3 8 Conclusion Be careful Learning how to use cookbook solutions is certainly an im portant objective Also to learn from case studies Read before Write is a good idea But struggling the way through an endless series of cookbook examples is definitely not the way to success 4 Spiral Approach 4 1 Definition of the Spiral Approach Bergin 2001 explains this approach as follows Topics in a course are divided up into fragments and the fragments introduced in an order that facilitates student prob lem solving Many of the fragments introduce a topic but do not cover it in detail J ust enough detail is given initially so as to form a basic understanding that can be applied to problem solving Additional cycles contain reinforcing fragments that go into more detail on the topic So there are two key elements that are crucial for the Spiral Approach 1 Divide the topics into fragments The
165. uctured and object oriented programmin Topics of object oriented programming Variables Method call and return Objects and object references Inheritance and polymorphism Objects Collabora tion 10 Writing Classes 10 2 Choosing in stance variables 10 4 The this key word using this to access hidden vari ables 10 4 The this key word using this as an argument or return value 10 10 Debugging 10 7 Adding class variables and Methods 10 4 The this key word 10 5 Writing con structors 10 1 Designing Classes 10 3 Designing Instance Methods 10 8 Reusing Code 11 Subclasses 11 4 Polymorphism 11 1 Inheritance 11 2 The protected access modifier 11 3 Overriding 11 4 Polymorphism 11 5 The Object class 11 6 Abstract classes 11 7 Final classes and methods 11 8 Inheritance in the AWT 12 The Abstract Window Toolkit 12 7 Creating and using components 12 2 Frames 12 3 Event Listeners how to implement an interface 12 2 Frames adding Components 12 4 Inner Classes 12 5 Attaching Listeners to multiple components 12 6 Layout 13 Data structures 13 3 Wrapper Classes 13 7 The String Buffer class 13 1 Multidimensional Arrays 13 2 The Vector class 13 6 Sets 14 Files 14 4 Advanced exception handling 14 5 Reading an writing data types 14 6 Reading and writing characters 14 7 Reading and
166. unexpected behaviour failure or of run time errors J ava s complete stack trace is recorded and can be checked for any failure or error 8 2 How Trainers Can Use Test Classes The trainer defines the specification for a class He sets up one or several test classes so that all mistakes that he expects from the trainees are checked It is important to give accurate feedback in case that a failure or error occurs The trainer asks the trainees to write the code of the class Trainees do their coding so that the specification set up by the trainer is met The J Unit Framework is very convenient for such trainings It gives the trainee a visual feedback complete access to the stack trace in case 49 8 3 8 4 8 5 8 6 8 7 Chapter 4 Existing solutions to overcome the problem of cognitive load of failures and the trainer can define a feedback text for any failure he expects Advantage of the Test Class Approach The trainer does not need a whole project The idea of a single class and its specifications are sufficient If the class should not use the existing API classes like Temperature that store the value of temperature Fraction that stores two integer values or Account that stores ac count numbers and the balance are good examples By setting up a test class you can show what specifications are and that specifications must be met and tested This can be done by the way without loosing time for long theo
167. up the code for instantiation But he can see what the command new does it constructs a new robot It places the robot at the place and in the direction specified in the constructor Later when one robot works together with others the student has not only to know how to construct a robot with a command line he also has to know how robots remember with whom they are working and how to forward commands to their colleagues Therefore it is preferable that the trainee already knows the schema of instantiation when he gets to this highly interrelated topic Conclusion Instantiating a robot manually teaches a fundamental schema early easily and figuratively and what is the most important separately from any other topic 5 Visualise the Exchange of Messages Without Splitted Attention 5 1 Method calls or the exchange of massages are a basic concept of both structured programming and object oriented programming There are two means to show the exchange of messages without split attention This can be done in a textbook or directly on the microworld Visualization in a Textbook Fig 19 King 2000 p 96 73 5 2 Chapter 6 Reducing cognitive load in Roboworld The figure above shows a good example to visualise method call and re turn value in a textbook According to split attention effect the explana tion would be better close to the arrows and not in a separate text Visualization in Existing Worlds The
168. vironment the cognitive load Semiotics emphasises that students must use different sign systems for real understanding But the sign systems must be introduced the way they can be integrated without overloading the working memory Reducing cognitive load will therefore not get in the way of other learning theories It will only refute some of their practices 98 Appendix A User Manual 1 1 Installation A J ava runtime environment must be installed at first Then 1 Copy the following two files to the same folder scenarios mws robow orld jar 2 With Windows operating system double click roboworld jar The application starts up and shows the list of the existing scenarios Mane Work of Holes Manage a 3 Select one of the scenarios Most evident examples are Demo of two collaborating robots Sender Listener 2 Listeners Inheritance key word super and Erroneous Robots with never ending execution About the scenario Sender Listener 2 Listeners you find further information on page 3 In all other examples robots are instantiated In the lower left part of the window you select a robot in the list Choose Robot and after that an operation in the list Choose Operation For instance Scenario Name Robot Operation Erroneous Robots ErroneousRobot 3 endlessLoop with never ending execution doSpecialT urn Demo of two collabo DemoRobot 5 doT

Introduction - TECFA - Université de Genève

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Introduction - TECFA - Université de Genève