编译原理笔记之词法分析器

package com.xawl.test;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.*;

public class WordImplements {
    
    /* * 1表示关键字 * 2表示标识符 * 3表示常数 * 4表示运算符 * 5表示界符 * 6表示字符串 * */

    //关键字
    static String []keyWord={
    "private","protected","public","abstract","class","extends","final","implements",
            "interface","native","new","static","strictfp","break","continue","return","do","while","if","else","for",
            "instanceof","switch","case","default","boolean","byte","char","double","float","int","long","short",
            "String","null","true","false","void","this","goto"};
    //运算符
    static String []operation={
    "+","-","*","/","%","++","--","-=","*=","/=","&","|","^","~","<<",">>",">>>","==","!=",
            ">","<","=",">=","<=","&&","||","!","."};
    //界符
    static String []symbol={
    ",",";",":","(",")","{","}"};
    static ArrayList<String> keyWords=null;
    static ArrayList<String> operations=null;
    static ArrayList<String> symbols=null;

    //指向当前所读到字符串的位置的指针
    static int p,lines;


    public static void main(String []args) throws FileNotFoundException {
    
        init();
        File file=new File("E:\\test.txt");
        lines=1;
        try(Scanner input=new Scanner(file)) {
    
            while (input.hasNextLine()){
    
                String str=input.nextLine();
                analyze(str);
                lines++;
            }
        }

    }

    //初始化把数组转换为ArrayList
    public static void init(){
    
        keyWords=new ArrayList<>();
        operations=new ArrayList<>();
        symbols=new ArrayList<>();
        Collections.addAll(keyWords, keyWord);
        Collections.addAll(operations, operation);
        Collections.addAll(symbols, symbol);
    }

    public static void analyze(String str){
    

        p=0;
        char ch;
        str=str.trim();
        for (;p<str.length();p++){
    
            ch=str.charAt(p);
            if (Character.isDigit(ch)){
    
                digitCheck(str);
            }else if (Character.isLetter(ch)||ch=='_'){
    
                letterCheck(str);
            }else if (ch=='"'){
    
                stringCheck(str);
            }
            else if (ch==' '){
    
                continue;
            }else {
    
                symbolCheck(str);
            }
        }
    }

    /*数字的识别 * 1、识别退出： * 1.1、遇到空格符 * 1.2、遇到运算符或者界符 * 2、错误情况： * 2.1、两个及以上小数点 * 2.2、掺杂字母 * */
    public static void digitCheck(String str){
    
        String token= String.valueOf(str.charAt(p++));
        //判断数字的小数点是否有且是否大于1
        int flag=0;
        boolean err=false;
        char ch;
        for (;p<str.length();p++) {
    
            ch = str.charAt(p);
            if (ch==' '||(!Character.isLetterOrDigit(ch)&&ch!='.')) {
    
                break;
            }else if (err){
    
                token+=ch;
            }
            else {
    
                token+=ch;
                if (ch == '.') {
    
                    if (flag == 1) {
    
                        err = true;
                    } else {
    
                        flag++;
                    }
                }else if (Character.isLetter(ch)){
    
                    err=true;
                }
            }
        }
        if (token.charAt(token.length()-1)=='.'){
    
            err=true;
        }
        if (err){
    
            System.out.println(lines+"line"+": "+token+" is wrong");
        }else {
    
            System.out.println("("+3+","+token+")");
        }
        if (p!=str.length()-1||(p==str.length()-1&&!Character.isDigit(str.charAt(p)))){
    
            p--;
        }
    }

    //标识符，关键字的识别
    public static void letterCheck(String str){
    
        String token= String.valueOf(str.charAt(p++));
        char ch;
        for (;p<str.length();p++){
    
            ch=str.charAt(p);
            if (!Character.isLetterOrDigit(ch)&&ch!='_'){
    
                break;
            }else{
    
                token+=ch;
            }
        }
        if (keyWords.contains(token)){
    
            System.out.println("("+1+","+token+")");
        }else {
    
            System.out.println("("+2+","+token+")");
        }
        if (p!=str.length()-1||(p==str.length()-1&&(!Character.isLetterOrDigit(str.charAt(p))&&str.charAt(p)!='_'))){
    
            p--;
        }
    }

    //符号的识别
    public static void symbolCheck(String str){
    
        String token= String.valueOf(str.charAt(p++));
        char ch;
        if (symbols.contains(token)){
    
            System.out.println("("+5+","+token+")");
            p--;
        }else {
    
            if (operations.contains(token)){
    
                if (p<str.length()){
    
                    ch=str.charAt(p);
                    if (operations.contains(token+ch)){
    
                        token+=ch;
                        p++;
                        if (p<str.length()){
    
                            ch=str.charAt(p);
                            if (operations.contains(token+ch)){
    
                                token+=ch;
                                System.out.println("("+4+","+token+")");
                            }else{
    
                                p--;
                                System.out.println("("+4+","+token+")");
                            }
                        }else{
    
                            System.out.println("("+4+","+token+")");
                        }
                    }else {
    
                        p--;
                        System.out.println("("+4+","+token+")");
                    }
                }
            }else {
    
                p--;
                System.out.println(lines+"line"+": "+token+" is wrong");
            }
        }
    }

    //字符串检查
    public static void stringCheck(String str){
    
        String token= String.valueOf(str.charAt(p++));
        char ch;
        for (;p<str.length();p++){
    
            ch=str.charAt(p);
            token+=ch;
            if (ch=='"'){
    
                break;
            }
        }
        if (token.charAt(token.length()-1)!='"'){
    
            System.out.println(lines+"line"+": "+token+" is wrong");
        }else {
    
            System.out.println("("+6+","+token+")");
        }
    }
}