Java Authoring Lexical Analyzer

The lexical analyzer is to scan a program to determine whether it is a keyword, identifier, constant, delimiter, operator. Generally divided into one character and the classic V;

Here I use the classic V, this lexical parser is written in Java;

/*
Reserved words | Keyword: 1
operator | operators: 2
Delimiter: 3
Identifier: 4
Constant: 5
No recognition: 6
*/

The main code is:

/*** This program is by reading the characters of the file into a character array, and then traversing the array, the characters are read * sorted and output *@author * */ Public classWordanalyze {PrivateString keyword[] = {"Break", "include", "Begin", "End", "if", "Else", "while", "switch"}; Private Charch; //determine if it is a keyword    BooleanIsKey (String str) { for(inti = 0;i < keyword.length;i++)        {            if(Keyword[i].equals (str))return true; }        return false; }    //determine if it is a letter    BooleanIsletter (CharLetter ) {        if(Letter >= ' a ' && letter <= ' z ') | | (Letter >= ' A ' && letter <= ' Z '))            return true; Else            return false; }    //determine if it is a number    BooleanIsDigit (CharDigit) {        if(Digit >= ' 0 ' && digit <= ' 9 ')            return true; Else            return false; }    //Lexical Analysis    voidAnalyzeChar[] chars) {String arr= "";  for(inti = 0;i< chars.length;i++) {ch=Chars[i]; Arr= ""; if(ch = = "| | ch = = ' \ t ' | | ch = = ' \ n ' | | ch = = ' \ r '){}            Else if(Isletter (ch)) { while(Isletter (ch) | |isdigit (CH)) {arr+=ch; CH= chars[++i]; }                //fallback one characteri--; if(IsKey (arr)) {//Key WordsSystem.out.println (arr+ "\t4" + "\ t keyword"); }                Else{                    //identifiersSystem.out.println (arr+ "\t4" + "\ T identifier"); }            }            Else if(IsDigit (ch) | | (ch = = '. ')))            {                 while(IsDigit (ch) | | (ch = = '. ') &&isdigit (chars[++i] )) {if(ch = = '. ') i--; Arr= arr +ch; CH= chars[++i]; }                //belongs to the unsigned constantSystem.out.println (arr+ "\t5" + "\ T constant"); }            Else Switch(CH) {//operator                 Case' + ': System.out.println (ch+ "\t2" + "\ t operator"); Break;  Case'-': System.out.println (ch+ "\t2" + "\ t operator"); Break;  Case' * ': System.out.println (ch+ "\t2" + "\ t operator"); Break;  Case'/': System.out.println (ch+ "\t2" + "\ t operator"); Break; // Delimiter                 Case' (': System.out.println (ch+ "\t3" + "\ t delimiter"); Break;  Case') ': System.out.println (ch+ "\t3" + "\ t delimiter"); Break;  Case' [': System.out.println (ch+ "\t3" + "\ t delimiter"); Break;  Case'] ': System.out.println (ch+ "\t3" + "\ T"); Break;  Case'; ': System.out.println (ch+ "\t3" + "\ t delimiter"); Break;  Case' {': System.out.println (ch+ "\t3" + "\ t delimiter"); Break;  Case'} ': System.out.println (ch+ "\t3" + "\ t delimiter"); Break; //operator                 Case=: {ch= chars[++i]; if(ch = = ' = ') System.out.println ("= =" + "\t2" + "\ t operator")); Else{System.out.println ("=" + "\t2" + "\ t operator"); I--; }                         } Break;  Case‘:‘: {ch= chars[++i]; if(ch = = ' = ') System.out.println (": =" + "\t2" + "\ t operator"); Else{System.out.println (":" + "\t2" + "\ t operator"); I--; }                         } Break;  Case' > ': {ch= chars[++i]; if(ch = = ' = ') System.out.println (">=" + "\t2" + "\ t operator"); Else{System.out.println (">" + "\t2" + "\ t operator"); I--; }                         } Break;  Case' < ': {ch= chars[++i]; if(ch = = ' = ') System.out.println ("<=" + "\t2" + "\ t operator"); Else{System.out.println ("<" + "\t2" + "\ t operator"); I--; }                         } Break; //No recognition                default: System.out.println (ch+ "\t6" + "\ T no identifier"); }        }    } Public Static voidMain (string[] args)throwsException {File file=NewFile ("E:\\data.txt");//defines a file object that is used to initialize the FileReaderFileReader reader =NewFileReader (file);//defines a FileReader object that is used to initialize the BufferedReader    intLength = (int) file.length (); //when defining a character array, you need to define one more, because the lexical analyzer will encounter a character that is read ahead, and if it is the last//The character is read, and if the next character is read, an out-of-bounds exception occurs    CharBuf[] =New Char[Length+1];    Reader.read (BUF);    Reader.close (); Newwordanalyze (). analyze (BUF); }}

Operation Result:

Java Authoring Lexical Analyzer