【编译原理】TEST递归下降演示

MyUtil.java

package Util;
 
import Value_Final.RRule;
 
public class MyUtil {
    /**
     * 判断字符串是否是关键字
     * @param key 要判断的字符串
     * @return 是否找到
     * */
    public static boolean isKeyValue(String key){
        for(int i=0;i< RRule.KEY_VALUE.length;i++){
            if(key.equals(RRule.KEY_VALUE[i])){
                return true;
            }
        }
        return false;
    }
    /**
     * 判断字符串是否是双分界符
     * @param key 要判断的字符串
     * @return 是否找到
     * */
    public static boolean isDoubleDivider(String key){
        for(int i=0;i< RRule.DOUBLE_DIVIDER.length;i++){
            if(key.equals(RRule.DOUBLE_DIVIDER[i])){
                return true;
            }
        }
        return false;
    }
    /**
     * 判断字符串是否是单分界符
     * @param key 要判断的字符串
     * @return 是否找到
     * */
    public static boolean isSignalDivider(String key){
        for(int i=0;i< RRule.SIGNAL_DIVIDER.length;i++){
            if(key.equals(RRule.SIGNAL_DIVIDER[i])){
                return true;
            }
        }
        return false;
    }
    /**
     * 判断字符串是否是字母还是数字
     * @param key
     * @return 1 是字母 0 是数字 -1 异常
     * */
    public static int isWordsOrNumber(char key){
        int number=(int)key;
        if((number>='A'&&number<='Z')||(number>='a'&&number<='z')){
            return 1;
        }else if(number>='0'&&number<='9'){
            return 0;
        }else {
            return -1;
        }
    }
    /**
     * 判断字符串是否是数字
     * @param ss
     * @return
     * */
    public static Boolean isNumber(String ss){
        for(int i=0;i<ss.length();i++){
            if(isWordsOrNumber(ss.charAt(i))!=0){
                return false;
            }
        }
        return true;
    }
}

RRule.java

package Value_Final;
 
/**
 * 一些常用变量规则
 * */
public class RRule {
    //关键字 规则
    public static final String[] KEY_VALUE={"abstract","assert","boolean","break","byte","case","catch","char",
            "class","const","continue","default","do","double","else","enum","extends","final","finally",
            "float","for","goto","if","implements","import","instanceof","int","interface","long","native",
            "long","native","new","package","private","protected","public","return","short","static","super",
            "switch","this","throw","throws","try","void","while"};
 
    public static final String[] SIGNAL_DIVIDER={"=","+","-","*","(",")","{","}",";",":",","};
    public static final String[] DOUBLE_DIVIDER={"==",">=","<=","!="};
 
}

Analysis,java

import Util.MyUtil;
 
import java.util.Scanner;
 
public class Analysis {
    public static void main(String[] args) {
        String inputCode=getInputString();
        String spiltItem[]=inputCode.split(" ");
        for(String item:spiltItem){
            if (MyUtil.isKeyValue(item)){
                System.out.println(item);//输出关键字
            }else if(MyUtil.isSignalDivider(item)){
                System.out.println(item);
            }else {//不是关键字则有可能是好几种情况
 
                if(item.contains(";")){//解析a+b=c;
                    String addstring="";
                    for(int i=0;i<item.length();i++){
                        if(MyUtil.isSignalDivider(item.charAt(i)+"")){//如果是单分隔符
                            System.out.println(item.charAt(i));
                            addstring="";
                            continue;
                        }
                        addstring=addstring+item.charAt(i);
                        if(MyUtil.isDoubleDivider(addstring)){//判断是不是双分隔符
                            System.out.println(item.charAt(i));
                            addstring="";
                            continue;
                        }
                        if(item.charAt(i+1)==';'){
                            if(MyUtil.isNumber(addstring)){
                                System.out.println("数字:"+addstring);
                            }else {
                                System.out.println("变量:"+addstring);
                            }
 
                            System.out.println(";");
                        }
                    }
                }
 
            }
        }
 
    }
 
    public static String getInputString() {
        System.out.println("请输入一段代码，并以最后一行为end结束");
        Scanner scanner = new Scanner(System.in);
        String firstLine = scanner.nextLine();
        StringBuffer ss = new StringBuffer(firstLine+" ");
        while (!firstLine.equals("end")) {
            firstLine = scanner.nextLine();
            ss.append(firstLine+" ");
        }
        scanner.close();
        System.out.println("读取的是"+ss.toString());
        return ss.toString().replace("end", "");
 
    }
}