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1. WebDirectoryScanner new StringReader this userInputs try while scanner zzAtEOF scanner yylex catch IOException ex ex printStackTrace this reportTextArea setText Report getReport The string passed to the scanner is assigned to a string object userInputs a class variable of class WebDirectory For the scanner class WebDirectoryScanner its constructor takes an object of InputReader class Since StringReader 1S a subclass of InputReader it can substitute it for the more general InputReader since input to the scanner is just contained in a string The object of WebDirectoryScanner created 1S scanner Scanner yylex 1s the method for actual scanning When the end of file is reached the state of the scanner scanner zzAtEOF 1S set to true to denote that the end of the string has been reached At this point it stops scanning and displays the content of the Report class found on the lower part of the application window This is achieved by calling this reportTextArea setText Report getReport 4 2 Generating the Scanner WebDirectoryScanner java To generate the scanner class the JFLex tool is executed by pointing to the file WebDirectoryScanner flex as in figure 6 Clicking the Generate button will display the following at the same time as it drops the generated file in the folder indicated in the output directory If errors were encountered the source of the errors will instead2. if then 0 Condition if then else 0l With facilities like this some regular expressions would have been possible or easier to write An example is the regular expression for strong password which could have been written as iS a ee a hr Lee Using the lookahead assertion it could have easily tracked the occurrence of digits lowercase and uppercase letters and even special symbols To add another character flag to our own version of regular expression using facilities provided by JFlex would have been very tedious Facilities for lookahead assertions should be included in later versions of JFlex As a sequel to the above this study found that trying to set the range for the length of the password field using the range specifier x y the JFlex tool was not terminating during code generation and the processes of constructing the DFAs was taking an infinite time Compared to the usual total generating time of about 500ms JFlex did not finish even after 25 minutes This happened after several trials until it was discovered that the range specifier 8 20 IJCSI International Journal of Computer Science Issues Vol 7 Issue 3 No 4 May 2010 20 www lJCSLorg which says that the password should be at least 8 characters in length and at most 20 characters was the cause of the non termination Hence the range specifier was not useful in this case JFlex also lacks the special range specifier x which indicates at least
3. be filled in so as to reflect the situation And the process goes on as in the listing below public static String getReport report clearing the string first of initial values if webUrlok report report Invalid Web URL field n if ipAddressOk report report Invalid IP Address field n if emailAddressOk report report Invalid E Mail Address field n if gsmPhoneNoOk report report Invalid GSM Number field n if strongPwdoOk report report Your Password Is Not Strong Have At Least One Digit One Uppercase And One Lowercase Letter n if securityQuestionoOk report report Your Question Is Not Complete Check It n if countryOk report report Invalid Country Name field n if timeZoneOk report report Invalid Time Zone field n if report report report SATISFACTORY reset all fields before exiting webUrlOk false ipAddressOk false emailAddressOk false gsmPhoneNoOk false strongPwdOk false securityQuestionOk false countryOk false timeZoneOk false return report IJCSI International Journal of Computer Science Issues Vol 7 Issue 3 No 4 May 2010 18 www lJCSLorg 4 1 The Scanning Process The following code embedded as the action code for clicking button Submit on the graphical user interface starts off sustains and terminates the process of scanning WebDirectoryScanner scanner new
4. be indicated on the Messages pane and the user would go back and correct the ill formed lexical specification B JFlex 1 4 2 aS o Quit Lexical specification CAMy JF lex WorksiWebDirectoryScanner flex i i Generate ee Options Output directory ClMy JFlex Works Browse a Messages Figure 6 Snapshot of JFlex at Code Generation Time Pei re x Lavical snecticaton Ci Je orks WebclrectorvScanner fey Browse Generate Output direcion Cwi Jle Norka Browse eSales li Reading Cs lly Jflex Vorks VebDizectoryocanner flex A Parsing took Lous Constructing NPA NFA construction took Lous p states in NA Converting NEA to DPA DEA construction took Ls Sus 45 states before minimization 212 states in minimized DFA Minimization took 3lus 1d file C y daler Works WebDirectoryncanmer java saved as Cly dPlex Works VebDirectocyncanmer java Venting code to Ciy J lex Wocks WebDirectorvacanner java Writing took 20dus werall scanner generation tine 13 404us errora D warnings generation finished successfully y Figure 7 Snapshot Showing JFlex Messages after Generation of Code JFlex generates exactly one file containing one class from the specification except another class in the first section of the lexical specification is declared IJCSI International Journal of Computer Science Issues Vol 7 Issue 3 No 4 May 2010 19 w
5. can both range from zero to nine When there is only one digit it can range from zero to nine The semantics of the IPADDRESS macro follows intuitively Examples of strings in this language include 127 0 0 0 192 168 5 6 255 255 78 10 10 0 1 11 3 3 E Mail Address The listing is as shown below EMAILADDRESS a z0 9_ a z0 9_ a z 2 6 IJCSI International Journal of Computer Science Issues Vol 7 Issue 3 No 4 May 2010 16 www lJCSLorg An e mail address is made up of a string consisting of a possible mix of lower case letters digits underscore separated by the symbol and ending with a dot and a string of lowercase letters of length ranging from two to six A closure i e 2 6 1S placed after the a z to show that the extension could repeat Examples of strings in this language include pfizer yahoo co uk james gmail com bluecollar 37 com emeks_rex tim net 3 4 GSM Number REEEREX GLopat GSM Number oe ince J GSMNUMBER 0 9 3 0 9 0 9 10 A regular expression that can match any GSM Global System for Mobile Communication number was implemented GSM numbers usually comprise of ten to eleven digits or twelve to thirteen digits if country code is included 3 5 Strong Password The definition of a strong password requires a string which contains at least one lowercase letter one uppercase letter and one digit A strong password module is shown below for FLAGONE FL
6. is especially important if the dot character class is used in some of the regular expressions The dot character class refers to all characters Class variables were not declared hence the and the counterpart 3 was not necessary 2 4 Macro Definitions These are included in the second section usually after the options A macro definition has the form macroidentifier regular expression A macro definition is a macro identifier letter followed by a sequence of letters digits or underscores that can later be used to reference the macro This is followed by optional white space followed by an followed by optional white space followed by a regular expression The regular expression on the right hand side must be well formed and must not contain the or operators S 8 9 IJCSI International Journal of Computer Science Issues Vol 7 Issue 3 No 4 May 2010 15 www lJCSLorg 2 4 1 The Macros of WebDirectoryScanner flex File Macros were defined for the Web URL IP Address E Mail Address GSM Number Strong Password Security Question Country and Time Zone 3 Analysis of the Lexical Specification for the Web Directory Scanner The breakdown of the associated macros is as follows 3 1 Web URL The URL Universal Resource Locator must point to a web page or a definite resource to be valid The following is a listing of the web URL module from the lex specification file KkKKK KEKKK
7. lower case letter an upper case letter and a digit If the user fails to enter password matching such specification the program should respond by alerting the user with appropriate message such as Your password is not strong Scanner Figure 1 Model of GUI Lexical Analysis for a Web Directorv Annlication The job of checking the validity of fields in our application thus properly falls to the lexical analyzer In this case the Graphical User Interface GUI form collects the user inputs constructs an input string from the input fields and user supplied values and channels the input string to the scanner The scanner matches each segment field of the input string against a regular expression and reports its observation The report is thus generated and fed back to the GUI for the user to see The user is allowed to correct any erroneous field as long as it appears The model for this application is shown in figure above Specifically the application in question see figure 2 is a Web Directory Form Web administrators could use it to organize the different administrative information they may have on the web sites they administer The web directory form thus forms but one module in a potential software This form could check the validity of the fields before they are forwarded to the database The fields checked in this case are as follows Web URL IP Address E Mail Address GSM Phone Number Global Strong Passwor
8. on Microsoft Windows operating system IJCSI International Journal of Computer Science Issues Vol 7 Issue 3 No 4 May 2010 14 www lJCSLorg 2 2 The structure of the lexical specification file The lexical specification file for JFlex consists of three parts divided by a single line starting with 3 8 10 User code oo CAC Options and declarations 2 9 oo Lexical rules 2 2 1 User Code The first part contains user code that is copied literally into the beginning of the source file of the generated scanner just before the scanner class is declared in the java code This is the place to insert package declarations and import statements 2 2 2 Options and Declarations The second part of the lexical specification contains options to customize the generated scanner JFlex directives and Java code to include in different parts of the scanner declarations of lexical states and macro definitions for use in the third section Lexical Rules Each JFlex directive must be placed at the beginning of a line starting with the 3 character 2 2 3 Lexical Rules This section is introduced by another set of 33 characters on a new line after all the intended macro definitions It contains a set of regular expressions and actions Java code that are executed when the scanner matches the associated regular expression 5 The lexical rules are also called transition rules An example is shown below EXP
9. x but no upper limit JFlex should therefore be optimized in subsequent versions so that the range specifier can be used in a practical situation The way the space character was implemented in JFlex is truly not the best The idea of defining a space character using is very obscure especially when it lies side by side other characters For example a zA z used in the COUNTRY macro The space character following the capital Z is not very clear The use of escape characters like s or the posix space for the space character might be a better approach JFlex does not check the Java code included in the user code section and in the lexical rules for correctness It is relatively straight forward to plug in the Java Compiler javac into the jflex tool so as to do a static check on the java codes routing the error messages to JFlex display so that the user can also correct the Java codes earlier on instead of waiting for a separate session at run time to start the debugging process We recommend the integration of a lightweight debugger into JFlex The only uses well foreseen and provided for by the creators of the JFlex tools have been for either standalone scenarios where the scanner can be run as a complete and separate application or a scenario where the scanner is used by an overlying parser in this case the scanning method returns a token periodically to the parser In our present use the scanner has to be con
10. AGTWO and FLAGTHREE respectively Possible strings in this language would include 234loRd socKk3vbn YmeLOl1d shu b5b1 eee Strong Password Module FLAGONE a z FLAGTWO A Z FLAGTHREE 0 9 STRONGPWD FLAGONE FLAGTWO FLAGTHREE FLAGONE FLAGTHREE FLAGTWO ELAGTWO 4 FLAGONE EFLAGTHREE EFLAGTWO O FLAGTHREE FLAGONE FLAGTHREE FLAGTWO FLAGONE FLAGTHREE 3 6 Security Question A string is considered to be a question when it ends with a question mark A regular expression for this is as follows SECURITYQUESTION 3 7 Country The only requirement for a country name in the regular expression is that it contains only characters from A through Z whether uppercase or lowercase The listing is as follows a Country Modu beso kickeserawes EA COUNTRY a zA Z Since the language is English special characters involving modifiers like dieresis would not be accepted at least in this version The space character is included in the character range 3 8 Time Zone a A EEEE Time Zone Modu Ss ic 5 dee dna Bee Seas ae TIMEZONE glG m M tIT SANESE TagO Z OOTAS ARLOT o T EaR Ae E eF The time zone whose regular expression listing is shown above expects a string beginning with gmt the case mixtures does not matter followed by
11. He is a member of IEEE Computer and Communication societies Maduka Attamah is currently a Researcher and Associate Lecturer in the Department of Computer Science University of Ibadan He is also serving in the ICT Unit of University of Ibadan as Systems Analyst and Software Engineer He holds a B Eng 2006 in Electronic Engineering from the University of Nigeria Nsukka and an M Sc 2009 in Computer Science from the University of Ibadan Nigeria
12. IJCSI International Journal of Computer Science Issues Vol 7 Issue 3 No 4 May 2010 ISSN Online 1694 0784 ISSN Print 1694 0814 Evaluation of JFlex Scanner Generator Using Form Fields Validity Checking Ezekiel Okike and Maduka Attamah School of Computer Studies Kampala International University Kampala 256 Uganda Department of Computer Science University of Ibadan Ibadan Oyo State 02 234 Nigeria Abstract Automatic lexical analyzer generators have been available for decades now with implementations targeted for C C languages The advent of such a tool targeted to the Java language opens up new horizons not just for the language users but for the Java platform and technology as a whole Work has also been done by the Java language developers to incorporate much of the theory of lexical analysis into the language This paper focuses on the application of the JFlex tool a Java based lexical analyzer towards the generation of a standalone class that will work as one more entity in a solution space The study application is a lexer that serves to check the validity of fields in a form Keywords Lexical Analyzer Complier Generators Java Language Validity Checking 1 Introduction A frequently encountered problem in real life application is that of checking the validity of field entries in a form For example a form field may require a user to enter a strong password which usually must contain at least one
13. KKKKKKKKKKHK WebURL Module WEBURL http www https www ftp ftpI tftp tftp Qa Cole Ova Lasz 4 2963 To the left of the assignment lies the name of the macro WEBURL to the right lies the regular expression defining this macro This regular expression defines all strings beginning with an optional http www https www ftp ftp or tftp tftp then followed by any string of one or more length followed by another dot and terminating with two to six characters Some of the strings in this language include www yahoo com https www allmp3 net ftp ftp glide com personal readme html www operators org review html The front slash is a meta symbol meaning that JFlex converts it as one of its own operating symbols The only way to use this symbol as a terminal in a regular expression is to escape it as follows that is a backslash the escape character followed by a front slash The same applies to the dot a meta symbol which stands for the universal set of all characters available to the particular flex specification this universal set is defined with the Younicode ascii etc in the options section To use the dot character as a terminal there is need to escape it All meta characters must receive the same treatment if they are intended to be used as terminals in the language in question The question mark is an optional closure w
14. R System out print ss Valid gt yytext 0 7 The above example means that if you match an expression display the expression such that the string Valid gt expression is on the output screen Thus the transition or lexical rule is what happens when a pattern defined by a regular expression is matched 2 3 Lexical Specification for the Web Directory Scanner The file containing the lexical specifications for this study is WebDirectoryScanner flex The user code section of this file is empty as there was no need for the package statement and the import statement The classes were made standalone and simply copied to an application directory Thus the specification file begins as follows ole ole ole public class WebDirectoryScanner 6standalone Q Sunicode ole To make the generated class accessible by other classes in separate applications the public option was used The class option specifies WebDirectoryScanner as the name of the generated scanner class The standalone option was used because the scanner would not be plugged into a parser The scanner is also required to throw out token information on the console at the background since the main view port for the user 1s the Graphical User Interface to be used as debugging information To ensure the character set constituting the terminals of the scanner is sufficient to consider any special character the unicode was formally activated This
15. an optional space or spaces followed by an optional plus or minus sign space or spaces and a number ranging from one through twelve Additional 13 is added for completeness the time zone dating is not symmetrical Finally the string ends with a country or region name with possible commas or semi colon as defined by the following part of the regular expression a zA Z 1 1 The pair of square brackets with a space in between is the syntax for adding the space character to our regular expression 3 9 Analysis of the Lexical Rules for the Web Directory Scanner The lexical or transition rules section forms the heart of the real usefulness of this scanner For any of the patterns matched the lexical rule updates a custom class Report java which keeps a record of whether each field is valid or not The report class has one class variable each is a boolean type for each field in the web directory form The class variable declarations in Report java are shown below public static String report public static boolean webUrlOk false public static boolean ipAddressOk false public static boolean emailAddressOk false public static boolean gsmPhoneNoOk false public static boolean strongPwdOk false public static boolean securityQuestionOk false public static boolean countryOk false public static boolean timeZoneOk false public static String SATISFACTORY All Fields Ar
16. as written in Java One of the consequences of this is that in order to use the tool you must have your Java Runtime Environment JRE well setup Other setup procedures for the JFlex tool are also required The setup of Jflex involves two major steps namely Installation of the JRE 3 4 and installation of JFlex 2 5 Following appropriate installation and configuration procedures the screenshot showing that Java is properly configured on the local machine is shown in figure 3 while the screenshot which shows that JFlex tool is well configured is shown in figure 4 m CTWIDOWStystemd2lmdve Microsoft Windows XP Version 5 1 2600 C Copyright 1985 2001 Microsoft Corp Documents and Settings Bodija javac sage Javar coptions gt cource files where possible options include Generate all debugging info genon Generate no debugging info q lines vars source Generate only some debugging info howarn Generate no warmngs verbose Qutput messages about what the compiler 15 doing deprecation Qutput source locations where deprecated APIS are used classpath path Specify where to find user class files and annotation processors cp path Specify where to find user class files and annotation processors sourcepath paths Specify where to find input source files bootclasspath paths Override location of bootstrap class files exties edirs Qverride location of installed extensions endorseddirs edirs Overrid
17. d Security Question Country Time Zone Thus a regular expression for the above fields in a single lexical specification file generates a single scanner Using Jflex Java Flex a scanner implementation in Java following a given lexical specification could be achieved It is also possible to achieve the implementation in other languages such as C or C with Lex or Flex which is a faster version of Lex 3 10 12 IJCSI International Journal of Computer Science Issues Vol 7 Issue 3 No 4 May 2010 13 www lJCSLorg Web URL IP Address E Mail Address Clear GSM Phone Number Submit Strong Password Next Security Question Country Time Zone Form Check Report Figure 2 Snapshot of the Web Directory Application This paper is thus focused on the use of the JFlex tool to generate a scanner for a language defined by the extended regular expression and supported by the JAVA programming language 2 The Method The development and evolution of Lex and Flex is described in 7 10 Originally these tools were developed for the UNIX operating system to generate scanners in the C programming language but afterwards versions for other operating systems and programming languages began to surface Popular Java versions of lex include JLex and JFlex Flex can be downloaded along with its documentation at 1 whereas JFlex can be downloaded at 2 JFlex w
18. e Satisfactory From all the fields in the form a single string is constructed and passed to the scanner for analysis IJCSI International Journal of Computer Science Issues Vol 7 Issue 3 No 4 May 2010 17 www lJCSLorg The string 1s constructed as follows Each value supplied by the user is concatenated to a string which stands for the title or identification for the field in which the entry was made For example if the user enters mathi yahoo com in the E Mail Address field then the string mathi yahoo com is concatenated to Email Address and terminated by a n to show the end of that segment or field And this yields Email Address mathi yahoo com n as the resulting string For the form shown below figure 5 the string passed to the scanner would be Web Url http www google com n IP Address 10 0 11 98 nEmail Address gmailadmin gmail com n GSMNumber 8938097865342 nStrong Password goGetMlicorsO0ft nSecurity Question How are you today n Country Moscow nTimeZone GMT 3 00 St Petersburg Volgograd n FS My Web Directory Porm ela UH IF Aikema E H Ail AHNITE R it Fhinn Bure Strang Pais Security uration a mone Fe Time Zonei Form Check Report Figure 5 Snapshot of Web Directory Application under Testing n is the escape character for new line When the scanner sees a new line it stops trying to recognize the pattern and compares what it already has to see if it is s
19. e location of endorsed standards path proc none only Control whether annotation processing and or compilation 15 done processor lt c assio eclass2 gt eclassd gt Names of the annotation processors to run bypasses default discovery process processorpath pathy Specify where to find annotation processors directory Specify where to place generated class files 5 rectory Specify where to place generated source files imlicity none class Specify whether or not to generate class files for implicitly referenced files encoding encoding Specify character encoding used by source files source rel ease Provide source compatibility with specified release target release Generate class files for specific W version version Version information help Print a synopsis of standard options Akey value Qptions to pass to annotation processors Print a synopsis of nonstandard options Jelay Pass flags directly to the runtime system Documents and Settings Bodija_ Figure 3 Snapshot That Shows That Java Is Well Configured On The Local Machine Figure 4 Snapshot Which Shows That Java JFlex Tool is Well Configured and Ready 2 1 The Lexical Specification for JFlex A lexical specification file was created from a text file txt by changing the extension of the file from txt to flex This implies that a specification file can be edited by simple text editors like notepad exe or wordpad exe both
20. hich indicates that its operand may be once or not be there at all The square brackets are used to define character sets in shorthand For example a z which implies one of a or b up to z The 2 6 is the range specifier which indicates that its operand in this case the character set a z can occur for a minimum of two times and a maximum of six times The meta symbol indicates iteration or closure This means that there can be at least one or more iterations the empty string is not possible The meta symbol indicates the Kleene closure which means that the iteration can occur zero or more times up to infinity the empty string is possible with the Kleene closure JFlex also uses the Java format for comments and as such comments can be contained in between and for multiline comments or after for single line comments 3 2 IP Address The listing 1s as shown below kTP Address Module KKKKKKKK KK KKK OCTET 0 1 0 9 0 9 E NE EAE E a 2 POs R LO 3 IPADDRESS OCTET OCTET OCTET OCTET An IP address has four octets each containing a number between O and 255 inclusive The OCTET macro defines this range and explained as follows when the first digit is a zero or one then the second and third digits can range from O through 9 When the first digit is two then the second and third digits can only range from zero through five When there are only two digits then they
21. neither standalone nor parser compatible can more easily utilize the scanner References 1 http www gnu org software flex 2 http www jflex de 3 http Jjava sun com javase 6 download jsp 4 http java sun com javase 6 webnotes install 5 JFlex User s Manual Version 1 4 2 May 27 2008 JF lex Installation Pack Accompanying Manual 6 The Regular Expression Cheat Sheet From www lLoveJackDaniels com 7 Compilers Principles Techniques and Tools Alfred V Aho et al of Ed Pearson Education Inc 2007 8 S Chattopadhayay Compiler Design New Delhi Prentice Hall xvii 225pp 2005 9 K D Cooper and L Torczon Engineering a Compiler New York MK xxx 801pp 2008 10 J Levine Flex and Bison text processing tools New York O Reilly Media pp304 2009 Ezekiel U Okike received the B Sc degree in Computer Science from the University of Ibadan Nigeria in 1992 the Master of Information Science MInfSc in 1995 and PhD in Computer Science in 2007 all from the same University He has been a lecturer in the Department of Computer Science University of Ibadan since 1999 till date Since September 2008 to date he has been on leave as a Senior Lecturer and Dean of the School of Computer Studies Kampala International University Uganda His current research interests are in the areas of Software Engineering Software Metrics Compilers and Programming Languages
22. scanner methods and fields accessible in the actions API can be found in 5 4 3 Compiling the Generated Scanner The generated scanner class is compiled using the Java compiler o CWINDOWS system32 emd exe Microsoft Windows XP Version 5 1 2600 C Copyright 1985 2001 Microsoft Corp C Documents and Settings Bodija gt cd C ocd Wy JFlex Works C Hy JFlex Worksejavac WebDirectoryScanner Java Figure 8 Screenshot Showing the Command for Compiling the Generated Code Pressing the Enter key in the command line will produce the file WebDirectoryScanner class which the Java Virtual Machine can then execute this assumes there were no errors in the codes otherwise debugging would be done first Other class files needed for this case study were Report class and WebDirectory class The entry point Main class to the entire application is in WebDirectory class Hence this class was passed to the Java Virtual Machine at the command line during start of execution 4 4 Evaluation of JFlex tool 4 4 1 Some Limitations of JFlex 1 4 2 Some of the observed limitations of Jflex from this study are as follows There are currently no provisions for assertions Assertions form part of the theory of the extended regular expression Some assertions are Lookahead assertion Negative lookahead Lookbehind assertion lt Negative lookbehind or lt Once only subexpression gt Condition
23. tent with just being one of the utility classes in the entire application The best bet is for it to standalone but then the field of the scanner that indicates that it has reached end of file zzAtEOF is a private member of the scanner class And JFlex does not generate accessor methods for this field Creating a non standalone scanner even makes matters worse because the scanner will be expecting to scan get a token return the token and then stop waiting for a call by a parser The class acting as the parser will have to look out for a predetermined integer in the returned tokens which denote an end of file from the scanner In our application we desired that the scanner scans through the entire input stream before returning And the calling class is not a parser The generated scanner had to be modified for this study application An accessor method for the zzAtKOF field was implemented so as to be able to track the end of file EOF as shown in the following code snippet WebDirectoryScanner scanner new WebDirectoryScanner new StringReader this userInputs cry A while scanner getZZAtEOF scanner yylex catch IOException ex The while statement will continue to execute the scanning method yylex while the end of file is not reached EOF 1S known when scanner getZzAtEOF method returns true We recommend that JFlex should generate public accessors for all the scanner fields so that applications that are
24. ufficient 4 Discussion Consider the transition rules below ole oe Web Url WEBURL n Report webUrlOk true TP Address IPADDRESS n Report ipAddressOk true Email Address EMATILADDRESS n Report emailAddressOk true GSM Number GSMNUMBER n Report gsmPhoneNoOk true Strong Password STRONGPWD n Report strongPwdOk true Security Question SECURITYQUESTION n Report securityQuestionOk true Country COUNTRY n Report countryOk true TimeZone TIMEZONE n Report timeZoneOk true When the scanner sees the constant string Web URL followed by another string that matches the pattern for WebURL WEBURL and a newline character then there is a valid WebURL field The webURL field of the Report class Report webUr10k will be set to true indicating that that field is valid This happens to the rest of the string At the end of the string zzAtEOF see also 4 1 all the fields of the Report class are inspected and if any of them 1s still false they are false by default then the scanner assumes that there is an error with the particular field An error message tied to the field or fields is displayed The following code snippet compiles the report string to be displayed on the Form Check Report pane if webUrlOk report report Invalid Web URL field n If the value of webUrlok is false the report string should
25. ww lJCSLorg The generated class contains among other things the DFA tables an input buffer the lexical states of the specification a constructor and the scanning method with the user supplied actions 5 The message pane shows that the DFA has a total of 455 states before minimization and a total of 212 states after minimization This is over 100 efficiency The class Yylex by default could be customizable with the class directive The input buffer of the scanner is connected with an input stream via the java io Reader object which is passed to the scanner in the generated constructor The main interface of the scanner to the outside world is the generated scanning method its default name yylex and its default return type yytoken Most of the generated class attributes are customizable name return type declared exceptions etc If yylex is called it will consume input until one of the expressions in the specification 1s matched or an error occurs If an expression is matched the corresponding action is executed immediately It may return a value of the specified return type in which case the scanning method returns with this value or if it does not return a value the scanner resumes consuming input until the next expression is matched When the end of file is reached the scanner executes the EOF action and also upon each further call to the scanning method returns the specified EOF value Details of the
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