1 int sum = 0; for(int i = 1; i <= 100; i = i + 1) sum += i;#

  1 package com.gxf.lexical;  2   3 import java.util.Scanner;  4   5 public class Lexical {  6     String input = "";                                        //源程序  7     String keyWords[] = {"int", "for"};                        //关键词  8     int point = 0;                                            //全局指针指向源程序  9     int syn = 0;                                            //单词种别码 10     int sum = 0;                                            //数字的总和 11     StringBuffer token = new StringBuffer("");                //存放单词 12      13     public static void main(String[] args) { 14         Scanner scanner = new Scanner(System.in); 15         Lexical lexical = new Lexical(); 16  17         lexical.input = scanner.nextLine(); 18 //        System.out.println(lexical.input);//输入源程序         19         scanner.close(); 20          21         do{ 22             lexical.scanner(); 23             switch(lexical.syn){ 24                 case 4: 25                     System.out.println("(" + lexical.syn + "," + lexical.sum + ")"); 26                     break; 27                     default: 28                         System.out.println("(" + lexical.syn + "," + lexical.token + ")"); 29                     break; 30             } 31         }while(lexical.syn != 17); 32     } 33      34     /** 35      * 词法分析器 36      */ 37     public void scanner(){ 38         //将单词置为空 39         token = new StringBuffer(); 40         while(‘ ‘ == input.charAt(point)) 41             point++;                                        //去掉空格 42         if((input.charAt(point) >= ‘a‘ && input.charAt(point) <= ‘z‘) || 43                 (input.charAt(point) >= ‘A‘ && input.charAt(point) <= ‘Z‘)){//关键词或者标识符 44             syn = 3;//种别码为3 45             while((input.charAt(point) >= ‘a‘ && input.charAt(point) <= ‘z‘) || 46                     (input.charAt(point) >= ‘A‘ && input.charAt(point) <= ‘Z‘) || 47                     (input.charAt(point) >= ‘0‘ && input.charAt(point) <= ‘9‘)){ 48                 token.append(input.charAt(point)); 49                 point++; 50             } 51 //            point--;//后退一个位置 52             for(int i = 0; i < keyWords.length; i++){ 53                 if(keyWords[i].equals(String.valueOf(token))){ 54                     syn = i + 1;//修改种别码 55                     break; 56                 } 57             } 58         }//if 59         else if(input.charAt(point) >= ‘0‘ && input.charAt(point) <= ‘9‘){//如果是数字 60             syn = 4; 61             sum = 0; 62             while(input.charAt(point) >= ‘0‘ && input.charAt(point) <= ‘9‘){ 63                 sum = sum * 10 + (input.charAt(point) - ‘0‘); 64                 point++; 65             } 66             //point--;//后退一个字符 67         }//else if 68         else{//其他字符 69             switch(input.charAt(point)){ 70                 case ‘>‘://大于符号 71                     token = new StringBuffer(">");//重置token 72                     point++; 73                     if(input.charAt(point) == ‘=‘){ 74                         token.append("="); 75                         syn = 10; 76                     }else{ 77                         syn = 9; 78                         point--; 79                     } 80                     point++; 81                     break; 82                 case ‘<‘: 83                     token = new StringBuffer("<"); 84                     point++; 85                     if(input.charAt(point) == ‘=‘){ 86                         token.append("="); 87                         syn = 12; 88                     }else{ 89                         syn = 11; 90                         point--; 91                     } 92                     point++; 93                     break; 94                 case ‘*‘: 95                     token = new StringBuffer("*"); 96                     syn = 5; 97                     point++; 98                     break; 99                 case ‘/‘:100                     token = new StringBuffer("/");101                     syn = 6;102                     point++;103                     break;104                 case ‘+‘:105                     token = new StringBuffer("+");106                     syn = 7;107                     point++;108                     break;109                 case ‘-‘:110                     token = new StringBuffer("-");111                     syn = 8;112                     point++;113                     break;114                 case ‘;‘:115                     token = new StringBuffer(";");116                     syn = 14;117                     point++;118                     break;119                 case ‘(‘:120                     token = new StringBuffer("(");121                     syn = 15;122                     point++;123                     break;124                 case ‘)‘:125                     token = new StringBuffer(")");126                     syn = 16;127                     point++;128                     break;129                 case ‘#‘:130                     token = new StringBuffer("#");131                     syn = 17;132                     point++;133                     break;134                 case ‘=‘:135                     token = new StringBuffer("=");136                     syn = 13;137                     point++;138                     break;139             }    140             141         }142     }143 }