编译原理：递归向下分析程序建立语法分析树的Java实现（二）

在上一篇文章中，我们已经得到了LL(1)文法，现在，我们使用java编写递归向下的语法分析程序开建立语法分析树。

当一个文法满足LL(1)条件时，我们就可以为它构造一不带回溯的自上而下的分析程序，这个分析程序时由一组递归过程组成的，每个过程对应文法的一个非终结符。

程序实现代码：

Main

public class Main {public static void main(String[] args) {Parser par = new Parser();Node root;root=par.parseTree();root.treePrint();}}

Node

import java.util.LinkedList; public class Node{public Token tok;private LinkedList<Node> cldList = new LinkedList<Node>();public Node(Token tok) { this.tok = tok; }//leafpublic void addCld(Node nd){cldList.add(nd);}public void treePrint(){treePrintLevel(this, 0);return;}private void treePrintLevel(Node nd, int level){int i;if(nd!=null) //root{for(i=0;i<4*level;i++)System.out.print("-");nd.tok.emitToken();}if(nd.cldList.isEmpty()==false) //recursive{for (Node currNd: nd.cldList) {  treePrintLevel(currNd, level+1);    }  }}}

Parser

public class Parser{private Scanner scnr;private Token currentToken;public Parser(){scnr = new Scanner();}public Node parseTree(){Node root;currentToken=scnr.getNextToken();root=program();if(currentToken.matchToken(Tag.END))return root;else{System.out.println("syntax error: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node program(){Node nProg=new Node(new Token(Tag.PRO));Node nBlock=block();nProg.addCld(nBlock);return nProg;}private Node block(){    Node nLB, nDecls, nStmts, nRB, nBlock;        nBlock=new Node(new Token(Tag.BLO));if(currentToken.matchToken(Tag.LB)){nLB=new Node(currentToken);currentToken=scnr.getNextToken();nDecls=decls();nStmts=stmts();if(currentToken.matchToken(Tag.RB)){nRB=new Node(currentToken);currentToken=scnr.getNextToken();nBlock.addCld(nLB);nBlock.addCld(nDecls);nBlock.addCld(nStmts);nBlock.addCld(nRB);return nBlock;}else{System.out.println("expecting }, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{System.out.println("expecting {, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node decls(){Node nDecls, nDecl, nDeclsCld, nEps;nDecls=new Node(new Token(Tag.DECLS));if(currentToken.matchToken(Tag.INT) || currentToken.matchToken(Tag.BOOL)){nDecl=decl();nDeclsCld=decls();nDecls.addCld(nDecl);nDecls.addCld(nDeclsCld);return nDecls;}else {nEps=new Node(new Token(Tag.EPS));nDecls.addCld(nEps);return nDecls;}}private Node decl(){Node nDecl, nType, nId, nSc;nDecl=new Node(new Token(Tag.DECL));if(currentToken.matchToken(Tag.INT) || currentToken.matchToken(Tag.BOOL)){nType=type();if(currentToken.matchToken(Tag.ID)){nId=new Node(currentToken);currentToken=scnr.getNextToken();if(currentToken.matchToken(Tag.SC)){nSc=new Node(currentToken);currentToken=scnr.getNextToken();nDecl.addCld(nType);nDecl.addCld(nId);nDecl.addCld(nSc);return nDecl;}else{System.out.println("expecting ;, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{System.out.println("expecting identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else {System.out.println("expecting type int or bool, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node type(){Node nType, nBasic, nTypep;nType = new Node(new Token(Tag.TYP));if(currentToken.matchToken(Tag.INT) || currentToken.matchToken(Tag.BOOL)){nBasic=basic();nTypep=typep();nType.addCld(nBasic);nType.addCld(nTypep);return nType;}else{System.out.println("expecting type int or bool, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node typep(){Node nTypep, nLsb, nNum, nRsb, nTypepCld, nEps;nTypep=new Node(new Token(Tag.TYPP));if(currentToken.matchToken(Tag.LSB)){nLsb=new Node(currentToken);currentToken=scnr.getNextToken();if(currentToken.matchToken(Tag.NUM)){nNum=new Node(currentToken);currentToken=scnr.getNextToken();if(currentToken.matchToken(Tag.RSB)){currentToken=scnr.getNextToken();nRsb=new Node(currentToken);nTypepCld=typep();nTypep.addCld(nLsb);nTypep.addCld(nNum);nTypep.addCld(nRsb);nTypep.addCld(nTypepCld);return nTypep;}else{System.out.println("expecting ], unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{System.out.println("expecting integer number, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}else{nEps=new Node(new Token(Tag.EPS));nTypep.addCld(nEps);return nTypep;}}private Node basic(){Node nBasic;nBasic = new Node(new Token(Tag.BASIC));if(currentToken.matchToken(Tag.INT) || currentToken.matchToken(Tag.BOOL)){nBasic.addCld(new Node(currentToken));currentToken=scnr.getNextToken();return nBasic;}else{System.out.println("expecting type int or bool, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node stmts(){Node nStmts, nStmt, nStmtsCld, nEps;nStmts=new Node(new Token(Tag.STMTS));if(currentToken.matchToken(Tag.IF) || currentToken.matchToken(Tag.WHILE) ||currentToken.matchToken(Tag.DO) ||currentToken.matchToken(Tag.BREAK) ||currentToken.matchToken(Tag.LB) ||currentToken.matchToken(Tag.ID) ){nStmt=stmt();nStmtsCld=stmts();nStmts.addCld(nStmt);nStmts.addCld(nStmtsCld);return nStmts;}else{nEps=new Node(new Token(Tag.EPS));nStmts.addCld(nEps);return nStmts;}}private Node stmt(){Node nStmt, nLoc, nSet, nBexpr, nIf, nLp, nRp, nStmtCld, nWhile, nDo, nBreak, nBlock, nSc;nStmt=new Node(new Token(Tag.STMT));if(currentToken.matchToken(Tag.IF)){nIf=new Node(currentToken);currentToken=scnr.getNextToken();if(currentToken.matchToken(Tag.LP)){nLp=new Node(currentToken);currentToken=scnr.getNextToken();nBexpr=bexpr();if(currentToken.matchToken(Tag.RP)){nRp=new Node(currentToken);currentToken=scnr.getNextToken();nStmtCld=stmt();nStmt.addCld(nIf);nStmt.addCld(nLp);nStmt.addCld(nBexpr);nStmt.addCld(nRp);nStmt.addCld(nStmtCld);return nStmt;}else{System.out.println("expecting ), unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{System.out.println("expecting (, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else if(currentToken.matchToken(Tag.WHILE)){nWhile=new Node(currentToken);currentToken=scnr.getNextToken();if(currentToken.matchToken(Tag.LP)){nLp=new Node(currentToken);currentToken=scnr.getNextToken();nBexpr=bexpr();if(currentToken.matchToken(Tag.RP)){nRp=new Node(currentToken);currentToken=scnr.getNextToken();nStmtCld=stmt();nStmt.addCld(nWhile);nStmt.addCld(nLp);nStmt.addCld(nBexpr);nStmt.addCld(nRp);nStmt.addCld(nStmtCld);return nStmt;}else{System.out.println("expecting ), unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{System.out.println("expecting (, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else if(currentToken.matchToken(Tag.DO)){nDo=new Node(currentToken);currentToken=scnr.getNextToken();nStmtCld=stmt();if(currentToken.matchToken(Tag.WHILE)){nWhile=new Node(currentToken);currentToken=scnr.getNextToken();if(currentToken.matchToken(Tag.LP)){nLp=new Node(currentToken);currentToken=scnr.getNextToken();nBexpr=bexpr();if(currentToken.matchToken(Tag.RP)){nRp=new Node(currentToken);currentToken=scnr.getNextToken();if(currentToken.matchToken(Tag.SC)){nSc=new Node(currentToken);currentToken=scnr.getNextToken();nStmt.addCld(nDo);nStmt.addCld(nStmtCld);nStmt.addCld(nWhile);nStmt.addCld(nLp);nStmt.addCld(nBexpr);nStmt.addCld(nRp);nStmt.addCld(nSc);return nStmt;}else{System.out.println("expecting ;, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{System.out.println("expecting ), unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{System.out.println("expecting (, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{System.out.println("expecting while, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else if(currentToken.matchToken(Tag.BREAK)){nBreak=new Node(currentToken);currentToken=scnr.getNextToken();if(currentToken.matchToken(Tag.SC)){nSc=new Node(currentToken);currentToken=scnr.getNextToken();nStmt.addCld(nBreak);nStmt.addCld(nSc);return nStmt;}else{System.out.println("expecting ;, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else if(currentToken.matchToken(Tag.LB)){nBlock=new Node(new Token(Tag.BLO));nBlock=block();nStmt.addCld(nBlock);return nStmt;}else if(currentToken.matchToken(Tag.ID)){nLoc=loc();if(currentToken.matchToken(Tag.SET)){nSet=new Node(currentToken);currentToken=scnr.getNextToken();nBexpr=bexpr();if(currentToken.matchToken(Tag.SC)){nSc=new Node(currentToken);currentToken=scnr.getNextToken();nStmt.addCld(nLoc);nStmt.addCld(nSet);nStmt.addCld(nBexpr);nStmt.addCld(nSc);return nStmt;}else{System.out.println("expecting ;, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{System.out.println("expecting =, unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{System.out.println("expecting one of if, while, do, break, { or identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node loc(){Node nLoc, nId, nLocp;nLoc=new Node(new Token(Tag.LOC));if(currentToken.matchToken(Tag.ID)){nId=new Node(currentToken);currentToken = scnr.getNextToken();nLocp=locp();nLoc.addCld(nId);nLoc.addCld(nLocp);return nLoc;}else{System.out.println("expecting identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node locp(){Node nLocp, nLsb, nAexpr, nRsb, nLocpCld, nEps;nLocp=new Node(new Token(Tag.LOCP));if(currentToken.matchToken(Tag.LSB)){nLsb=new Node(currentToken);currentToken=scnr.getNextToken();nAexpr=aexpr();if(currentToken.matchToken(Tag.RSB)){nRsb=new Node(currentToken);currentToken=scnr.getNextToken();nLocpCld=locp();nLocp.addCld(nLsb);nLocp.addCld(nAexpr);nLocp.addCld(nRsb);nLocp.addCld(nLocpCld);return nLocp;}else{System.out.println("expecting ], unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else{nEps=new Node(new Token(Tag.EPS));nLocp.addCld(nEps);return nLocp;}return null;}private Node bexpr(){Node nBexpr, nJoin, nBexprp;nBexpr=new Node(new Token(Tag.BEXP));if(currentToken.matchToken(Tag.NOT) ||currentToken.matchToken(Tag.SUB) ||currentToken.matchToken(Tag.LP) ||currentToken.matchToken(Tag.TRUE) ||currentToken.matchToken(Tag.FALSE) ||currentToken.matchToken(Tag.NUM) ||currentToken.matchToken(Tag.ID) ){nJoin=join();nBexprp=bexprp();nBexpr.addCld(nJoin);nBexpr.addCld(nBexprp);return nBexpr;}else{System.out.println("expecting one of !, -, (, true, false, number or identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node bexprp(){Node nBexprp, nOr, nJoin, nBexprpCld, nEps;nBexprp=new Node(new Token(Tag.BEXPP));if(currentToken.matchToken(Tag.OR)){nOr=new Node(currentToken);currentToken=scnr.getNextToken();nJoin=join();nBexprpCld=bexprp();nBexprp.addCld(nOr);nBexprp.addCld(nJoin);nBexprp.addCld(nBexprpCld);return nBexprp;}else{nEps=new Node(new Token(Tag.EPS));nBexprp.addCld(nEps);return nBexprp;}}private Node join(){Node nJoin, nEqu, nJoinp;nJoin=new Node(new Token(Tag.JOIN));if(currentToken.matchToken(Tag.NOT) ||currentToken.matchToken(Tag.SUB) ||currentToken.matchToken(Tag.LP) ||currentToken.matchToken(Tag.TRUE) ||currentToken.matchToken(Tag.FALSE) ||currentToken.matchToken(Tag.NUM) ||currentToken.matchToken(Tag.ID) ){nEqu=equality();nJoinp=joinp();nJoin.addCld(nEqu);nJoin.addCld(nJoinp);return nJoin;}else{System.out.println("expecting one of !, -, (, true, false, number or identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node joinp(){Node nJoinp, nAnd, nEqu, nJoinpCld, nEps;nJoinp=new Node(new Token(Tag.JOINP));if(currentToken.matchToken(Tag.AND)){nAnd=new Node(currentToken);currentToken=scnr.getNextToken();nEqu=equality();nJoinpCld=joinp();nJoinp.addCld(nAnd);nJoinp.addCld(nEqu);nJoinp.addCld(nJoinpCld);return nJoinp;}else{nEps=new Node(new Token(Tag.EPS));nJoinp.addCld(nEps);return nJoinp;}}private Node equality(){Node nEqu, nRel, nEqup;nEqu=new Node(new Token(Tag.EQU));if(currentToken.matchToken(Tag.NOT) ||currentToken.matchToken(Tag.SUB) ||currentToken.matchToken(Tag.LP) ||currentToken.matchToken(Tag.TRUE) ||currentToken.matchToken(Tag.FALSE) ||currentToken.matchToken(Tag.NUM) ||currentToken.matchToken(Tag.ID) ){nRel=rel();nEqup=equalityp();nEqu.addCld(nRel);nEqu.addCld(nEqup);return nEqu;}else{System.out.println("expecting one of !, -, (, true, false, number or identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node equalityp(){Node nEqup, nEq, nNe, nRel, nEqupCld, nEps;nEqup=new Node(new Token(Tag.EQUP));if(currentToken.matchToken(Tag.EQ)){nEq=new Node(currentToken);currentToken=scnr.getNextToken();nRel=rel();nEqupCld=equalityp();nEqup.addCld(nEq);nEqup.addCld(nRel);nEqup.addCld(nEqupCld);return nEqup;}else if(currentToken.matchToken(Tag.NE)){nNe=new Node(currentToken);currentToken=scnr.getNextToken();nRel=rel();nEqupCld=equalityp();nEqup.addCld(nNe);nEqup.addCld(nRel);nEqup.addCld(nEqupCld);return nEqup;}else{nEps=new Node(new Token(Tag.EPS));nEqup.addCld(nEps);return nEqup;}}private Node rel(){Node nRel, nAexpr, nRelp;nRel=new Node(new Token(Tag.REL));if(currentToken.matchToken(Tag.NOT) ||currentToken.matchToken(Tag.SUB) ||currentToken.matchToken(Tag.LP) ||currentToken.matchToken(Tag.TRUE) ||currentToken.matchToken(Tag.FALSE) ||currentToken.matchToken(Tag.NUM) ||currentToken.matchToken(Tag.ID) ){nAexpr=aexpr();nRelp=relp();nRel.addCld(nAexpr);nRel.addCld(nRelp);return nRel;}else{System.out.println("expecting one of !, -, (, true, false, number or identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node relp(){Node nRelp, nLt, nLe, nGt, nGe, nAexpr, nEps;nRelp=new Node(new Token(Tag.RELP));if(currentToken.matchToken(Tag.LT)){nLt=new Node(currentToken);currentToken=scnr.getNextToken();nAexpr=aexpr();nRelp.addCld(nLt);nRelp.addCld(nAexpr);return nRelp;}else if(currentToken.matchToken(Tag.LE)){nLe=new Node(currentToken);currentToken=scnr.getNextToken();nAexpr=aexpr();nRelp.addCld(nLe);nRelp.addCld(nAexpr);return nRelp;}else if(currentToken.matchToken(Tag.GT)){nGt=new Node(currentToken);currentToken=scnr.getNextToken();nAexpr=aexpr();nRelp.addCld(nGt);nRelp.addCld(nAexpr);return nRelp;}else if(currentToken.matchToken(Tag.GE)){nGe=new Node(currentToken);currentToken=scnr.getNextToken();nAexpr=aexpr();nRelp.addCld(nGe);nRelp.addCld(nAexpr);return nRelp;}else{nEps=new Node(new Token(Tag.EPS));nRelp.addCld(nEps);return nRelp;}}private Node aexpr(){Node nAexpr, nTerm, nAexprp;nAexpr=new Node(new Token(Tag.AEXP));if(currentToken.matchToken(Tag.NOT) ||currentToken.matchToken(Tag.SUB) ||currentToken.matchToken(Tag.LP) ||currentToken.matchToken(Tag.TRUE) ||currentToken.matchToken(Tag.FALSE) ||currentToken.matchToken(Tag.NUM) ||currentToken.matchToken(Tag.ID) ){nTerm=term();nAexprp=aexprp();nAexpr.addCld(nTerm);nAexpr.addCld(nAexprp);return nAexpr;}else{System.out.println("expecting one of !, -, (, true, false, number or identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node aexprp(){Node nAexprp, nAexprpCld, nAdd, nSub, nTerm, nEps;nAexprp=new Node(new Token(Tag.AEXPP));if(currentToken.matchToken(Tag.ADD)){nAdd=new Node(currentToken);currentToken=scnr.getNextToken();nTerm=term();nAexprpCld=aexprp();nAexprp.addCld(nAdd);nAexprp.addCld(nTerm);nAexprp.addCld(nAexprpCld);return nAexprp;}else if(currentToken.matchToken(Tag.SUB)){nSub=new Node(currentToken);currentToken=scnr.getNextToken();nTerm=term();nAexprpCld=aexprp();nAexprp.addCld(nSub);nAexprp.addCld(nTerm);nAexprp.addCld(nAexprpCld);return nAexprp;}else{nEps=new Node(new Token(Tag.EPS));nAexprp.addCld(nEps);return nAexprp;}}private Node term(){Node nTerm, nUnary, nTermp;nTerm = new Node(new Token(Tag.TERM));if(currentToken.matchToken(Tag.NOT) ||currentToken.matchToken(Tag.SUB) ||currentToken.matchToken(Tag.LP) ||currentToken.matchToken(Tag.TRUE) ||currentToken.matchToken(Tag.FALSE) ||currentToken.matchToken(Tag.NUM) ||currentToken.matchToken(Tag.ID) ){nUnary=unary();nTermp=termp();nTerm.addCld(nUnary);nTerm.addCld(nTermp);return nTerm;}else{System.out.println("expecting one of !, -, (, true, false, number or identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node termp(){Node nTermp, nTermpCld, nMul, nDiv, nUnary, nEps;nTermp = new Node(new Token(Tag.TERMP));if(currentToken.matchToken(Tag.MUL)){nMul=new Node(currentToken);currentToken=scnr.getNextToken();nUnary=unary();nTermpCld=termp();nTermp.addCld(nMul);nTermp.addCld(nUnary);nTermp.addCld(nTermpCld);return nTermp;}else if(currentToken.matchToken(Tag.DIV)){nDiv=new Node(currentToken);currentToken=scnr.getNextToken();nUnary=unary();nTermpCld=termp();nTermp.addCld(nDiv);nTermp.addCld(nUnary);nTermp.addCld(nTermpCld);return nTermp;}else{nEps=new Node(new Token(Tag.EPS));nTermp.addCld(nEps);return nTermp;}}private Node unary(){Node nUnary, nNot, nSub, nUnaryCld, nFac;nUnary = new Node(new Token(Tag.UNY));if(currentToken.matchToken(Tag.NOT)){nNot=new Node(currentToken);currentToken=scnr.getNextToken();nUnaryCld=unary();nUnary.addCld(nNot);nUnary.addCld(nUnaryCld);return nUnary;}else if(currentToken.matchToken(Tag.SUB)){nSub=new Node(currentToken);currentToken=scnr.getNextToken();nUnaryCld=unary();nUnary.addCld(nSub);nUnary.addCld(nUnaryCld);return nUnary;}else if(currentToken.matchToken(Tag.LP) ||currentToken.matchToken(Tag.TRUE) ||currentToken.matchToken(Tag.FALSE) ||currentToken.matchToken(Tag.NUM) ||currentToken.matchToken(Tag.ID) ){nFac=factor();nUnary.addCld(nFac);return nUnary;}else{System.out.println("expecting one of !, -, (, true, false, number or identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}private Node factor(){Node nFac, nLp, nRp, nBexpr, nLoc, nNum, nTrue, nFalse;nFac=new Node(new Token(Tag.FAC));if(currentToken.matchToken(Tag.LP)){nLp=new Node(currentToken);currentToken=scnr.getNextToken();nBexpr=bexpr();if(currentToken.matchToken(Tag.RP)){nRp=new Node(currentToken);currentToken=scnr.getNextToken();nFac.addCld(nLp);nFac.addCld(nBexpr);nFac.addCld(nRp);return nFac;}else{System.out.println("expecting ), unmatched: line " + scnr.line); //errorSystem.exit(-1);}}else if(currentToken.matchToken(Tag.ID)){nLoc=loc();nFac.addCld(nLoc);return nFac;}else if(currentToken.matchToken(Tag.NUM)){nNum=new Node(currentToken);currentToken=scnr.getNextToken();nFac.addCld(nNum);return nFac;}else if(currentToken.matchToken(Tag.TRUE)){nTrue=new Node(currentToken);currentToken=scnr.getNextToken();nFac.addCld(nTrue);return nFac;}else if(currentToken.matchToken(Tag.FALSE)){nFalse=new Node(currentToken);currentToken=scnr.getNextToken();nFac.addCld(nFalse);return nFac;}else{System.out.println("expecting one of (, true, false, number or identifier, unmatched: line " + scnr.line); //errorSystem.exit(-1);}return null;}}

Scanner

public class Scanner{public int line=1;private char ch;private int asc;private boolean getNext=true;private SymTable tbl; public Scanner(){tbl = new SymTable(); //initialize symbol table}private void getNextChar(){try{asc=System.in.read();}catch(Exception ex){}ch=(char)asc;}public Token getNextToken() {if(getNext)getNextChar();elsegetNext=true;while(ch==' ' || ch=='\t' || ch=='\r' || ch=='\n'){if(ch=='\n')line++;getNextChar();}if(ch=='&'){getNextChar();if(ch=='&')     //match &&return (new Token(Tag.AND));else{System.out.println("missing &: line" + line); //errorSystem.exit(-1);}}else if(ch=='|'){getNextChar();if(ch=='|')     //match ||return (new Token(Tag.OR));else{System.out.println("missing |: line " + line); //errorSystem.exit(-1);}}else if(ch=='='){getNextChar();  //look aheadif(ch=='=')     //match ==return (new Token(Tag.EQ));else{getNext=false;return (new Token(Tag.SET));}}else if(ch=='!'){getNextChar(); //look aheadif(ch=='=')     //match !=return (new Token(Tag.NE));else{getNext=false;return (new Token(Tag.NOT));}}else if(ch=='<'){getNextChar();  //look aheadif(ch=='=')     //match <=return (new Token(Tag.LE));else{getNext=false;return (new Token(Tag.LT));}}else if(ch=='>'){getNextChar(); //look aheadif(ch=='=')     //match >=return (new Token(Tag.GE));else{getNext=false;return (new Token(Tag.GT));}}else if(ch=='+')return (new Token(Tag.ADD));else if(ch=='-')return (new Token(Tag.SUB));else if(ch=='*')return (new Token(Tag.MUL));else if(ch=='/')return (new Token(Tag.DIV));else if(ch=='(')return (new Token(Tag.LP));else if(ch==')')return (new Token(Tag.RP));else if(ch=='{')return (new Token(Tag.LB));else if(ch=='}')return (new Token(Tag.RB));else if(ch=='[')return (new Token(Tag.LSB));else if(ch==']')return (new Token(Tag.RSB));else if(ch==';')return (new Token(Tag.SC));else if(ch=='$')return (new Token(Tag.END));else if( Character.isDigit(ch) ) {       int v = 0;       do {          v = 10*v + Character.digit(ch, 10);           getNextChar();       } while( Character.isDigit(ch) );        getNext=false;       return (new Token(Tag.NUM, Integer.toString(v)));       }else if( Character.isLetter(ch) ) {       StringBuffer b = new StringBuffer(); //string buffer      do {         b.append(ch);          getNextChar();       } while( Character.isLetterOrDigit(ch) );       getNext=false;String s = b.toString();int tag=tbl.find(s);       if(tag<0) {tbl.reserve(s, Tag.ID); //insert to symbol tablereturn (new Token(Tag.ID, s));}else if(tag==Tag.ID)return (new Token(Tag.ID, s));elsereturn (new Token(tag));}else{System.out.println("Lexical error: line "+line+", "+ch);System.exit(-1);}return null;}//end-of-getToken}

SymTable

import java.util.Hashtable;public class SymTable{//symbol table    private Hashtable<String, Integer> stbl;public void reserve(String key, int value) { stbl.put(key, value); }  public SymTable(){stbl = new Hashtable<String, Integer>();reserve("if", Tag.IF);      reserve("else", Tag.ELSE);      reserve("while", Tag.WHILE);      reserve("do", Tag.DO);      reserve("break", Tag.BREAK);reserve("true", Tag.TRUE);reserve("false", Tag.FALSE);      reserve("int", Tag.INT);      reserve("bool", Tag.BOOL);}public Integer find(String s){if(stbl.get(s)==null)return -1;else return stbl.get(s);}}

Tag

public class Tag {public final static int  IF=256, ELSE=257, WHILE=258, DO=259, BREAK=260,  //keyword  TRUE=261, FALSE=262,                             //boolean constant  INT=263, BOOL=264,                               //type  AND=265, OR=266, NOT=267,                        //boolean operator  EQ=268, NE=269, GT=270, GE=271, LT=272, LE=273,  //relational operator  SET=274,                                         //assignment  ADD=275, SUB=276, MUL=277, DIV=278,    //arithmetic operator  SC=279, LP=280, RP=281, LB=282, RB=283,          //delimiter  LSB=284, RSB=285,                                //delimiter  ID=286,                                          //identifier  NUM=287, //integer-number    PRO=300,   //program  BLO=301,   //block  DECLS=302, //declarations  DECL=303,  //declaration  TYP=304,   //type  TYPP=305,  //type'  BASIC=306, //basic    STMTS=307, //statements    STMT=308,  //statement  LOC=309,   //location  LOCP=310,  //location'    BEXP=311,  //boolean expression  BEXPP=312, //boolean'  JOIN=313,  //join  JOINP=314, //join'  EQU=315,   //equality  EQUP=316,  //equality'  REL=317,   //relation  RELP=318,  //relation'  AEXP=319,  //arithmetic  AEXPP=320, //arithmetic'  TERM=321,  //term  TERMP=322, //term'  UNY=323,   //unary  FAC=324,   //factor  EPS=325,   //epsilon    END=326;   //$}

Token

public class Token{public final int tag;public String value;public Token(int t){tag=t; value="";}public Token(int t, String v) { tag = t; value = v;}public boolean matchToken(int tag){if(this.tag==tag)return true;elsereturn false;}public void emitToken(){ System.out.println("<" + tag + ", " + value + ">"); }}

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