递归下降法实现语法分析器（java）

import java.io.*; import java.util.*; public class Scanning { //存放识别出的token private ArrayList<Token> lt = new ArrayList<Token>(); //记录取出的token个数 private static int i=0; //存放所有关键字 private static final String[] reserveWord={"if","else","int","return","void","while"}; //存放源程序路径 private String dir; //记录行号 private static int lineCount=0; //源文件每行代码的字符数组的下标，指向当前分析的下一个字符 private int index=0; private String token; //注释起止标志 private boolean isComm = false; //构造方法 public Scanning(String dir) { this.dir=dir; } //词法分析的算法实现 public void scanAll(){ File f=new File(dir); try { if(!f.exists()) { System.out.println("源文件不存在"); } else { BufferedReader br=new BufferedReader(new FileReader(dir)); String s; //开始词法分析，源文件一行一行地读入 while((s=br.readLine())!=null){ lineCount++; //过滤行字符串，截去字符串开头和末尾的空白 s = s.trim(); System.out.println(lineCount + ":" + s); //将每行的字符串转为字符数组 char[] c = s.toCharArray(); //将此行源代码一个字符一个字符地扫描 while(index < c.length){ token = " "; char ch = this.getChar(c); switch(ch){ //此字符为字母 case 'a':case 'b':case 'c':case 'd':case 'e':case 'f':case 'g':case 'h':case 'i':case 'j':case 'k':case 'l': case 'm':case 'n':case 'o':case 'p':case 'q':case 'r':case 's':case 't':case 'u':case 'v':case 'w':case 'x': case 'y':case 'z':case 'A':case 'B':case 'C':case 'D':case 'E':case 'F':case 'G':case 'H':case 'I':case 'J': case 'K':case 'L':case 'M':case 'N':case 'O':case 'P':case 'Q': case 'R':case 'S':case 'T':case 'U':case 'V':case 'W':case 'X':case 'Y':case 'Z': token = this.contact(token, ch); if(index == c.length){ //全部由字母组成，token判断为id if(!isComm) lt.add(new Token("id",token,lineCount)); break; }else{ ch=this.getNextChar(c); while(this.isLetter(ch)){ token=this.contact(token, ch); if(index==c.length) break; else ch=this.getNextChar(c); } } //回退一个字符的位置 if(index <= c.length) this.retract(); //判断此字符串为标识符 token=token.trim(); //检查此字符串是否为保留字 if(this.isReserve(token)){ if(!isComm) System.out.println(" " + " " + "reserved word:" + token); if(!isComm) lt.add(new Token(token,token,lineCount)); }else{ if(!isComm) System.out.println(" " + " " + "ID: " + token ); if(!isComm) lt.add(new Token("id",token,lineCount)); } token=" "; break; //此字符为数字 case '0':case '1':case '2':case '3':case '4':case '5':case '6':case '7':case '8': case '9': token=this.contact(token, ch); if(index==c.length){ if(!isComm) lt.add(new Token("num",token,lineCount)); break; }else{ ch=this.getNextChar(c); while(this.isDigit(ch)){ token=this.contact(token, ch); if(index==c.length) break; else ch=this.getNextChar(c); } } if(index<=c.length) this.retract(); //判断此字符串为数字 token = token.trim(); if(!isComm) System.out.println(" " + " " + "num: " + token ); if(!isComm) lt.add(new Token("num", token, lineCount)); token=" "; break; case '=': token=this.contact(token, ch); ch=this.getNextChar(c); //如果下一个字符为 = ，则为关系运算符 if(ch=='='){ index ++; token=this.contact(token, ch); if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token ); if(!isComm) lt.add(new Token("relop",token,lineCount)); }else{ if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token ); if(!isComm) lt.add(new Token("equalop",token,lineCount)); } this.retract(); token=" "; break; case '!': token=this.contact(token, ch); ch=this.getNextChar(c); //如果下一个字符为=，则为不等号 if(ch=='='){ index ++; token=this.contact(token, ch); if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token); if(!isComm) lt.add(new Token("relop",token,lineCount)); } this.retract(); token=" "; break; case '<': token=this.contact(token, ch); ch=this.getNextChar(c); if(ch=='='){ index++; token=this.contact(token, ch); if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token); if(!isComm) lt.add(new Token("relop",token,lineCount)); }else{ if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token); if(!isComm) lt.add(new Token("relop",token,lineCount)); } this.retract(); token=" "; break; case '>': token=this.contact(token, ch); ch=this.getNextChar(c); if(ch=='='){ index++; token=this.contact(token, ch); if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token ); if(!isComm) lt.add(new Token("relop",token,lineCount)); }else{ if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token ); if(!isComm) lt.add(new Token("relop",token,lineCount)); } this.retract(); token=" "; break; case '+': token=this.contact(token, ch); if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token ); if(!isComm) lt.add(new Token("addop",token,lineCount)); token=" "; break; case '-': token=this.contact(token, ch); if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token ); if(!isComm) lt.add(new Token("addop",token,lineCount)); token=" "; break; case '/': token=this.contact(token, ch); ch=this.getNextChar(c); //如果下一个字符为 * ，则为注释符号 if(ch=='*'){ index ++; isComm=true; }else{ if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token ); if(!isComm) lt.add(new Token("mulop",token,lineCount)); } this.retract(); token=" "; break; case '*': token=this.contact(token, ch); ch=this.getNextChar(c); //如果下一个字符为 / ，则为注释符号 if(ch=='/'){ index ++; isComm=false; }else{ if(!isComm) System.out.println(" " + " " + "SpecialSymbol: " + token ); if(!isComm) lt.add(new Token("mulop",token,lineCount)); } this.retract(); token=" "; break; case '(': token=this.contact(toke