词法分析学习-手工构词

这个是看MOOC学编译原理的一个作业。

识别标识符和关键字，核心在于转移图，dfa的构造

package bingone;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;

/**
 * 手工构造词法分析器，标注的关键字有if for 。
 * @author bingone
 *
 */
enum Token{
    FOR("for"),
    IF("if");
    String name;
    private Token(String name){
        this.name = name;
    }
}
public class ManualToken {
    /**
     * 对应转移图有 空 0, i 1, if 2,f 3,fo 4, for,5, 其他 6
     * @param row
     * @param str
     */
    private static void solve(int row,String str){
        int cnt = 0;
        int tag = 0;
        str = new String(str+" ");
        char [] token = new char[100];
        for(int i = 0;i<str.length();i++){
            char ch = str.charAt(i);
            if(ch ==‘ ‘){
                if(tag != 0){
                    if(tag==6){
                        System.out.print( "ID("+new String(token, 0, cnt) +")");
                    }else if(tag==2){
                        System.out.print(Token.IF);
                    }else if(tag==5){
                        System.out.print(Token.FOR);
                    }
                    System.out.println( "("+row+","+ (i-cnt+1) + ")" );
                }
                cnt = 0;
                tag = 0;
                continue;
            }
            token[cnt++] = ch;
            if(tag == 0){
                switch(ch){
                    case ‘i‘:tag = 1;break;
                    case ‘f‘:tag = 3;break;
                    default: tag = 6;break;
                }
            }else if(tag == 1){
                if(ch==‘f‘) tag = 2;
                else tag = 6;
            }else if(tag ==2) tag = 6;
             else if(tag==3){
                if(ch==‘o‘) tag = 4;
                else tag = 6;
            }else if(tag==4){
                if(ch==‘r‘) tag = 5;
                else tag = 6;
            }
        }
    }
    public static void main(String[] args) throws Exception {
//      System.out.println(System.getProperty("user.dir"));
        BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("./src/bingone/in.txt"))) ;
        String aline = null;
        int row = 1;
        while((aline = br.readLine()) != null){
            solve(row++,aline);
        }
    }
}