import parser.Parser;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        // 关键词
        List<String> keyList = new ArrayList<>(Arrays.asList("int","String"));
        // 关键词数
        List<Integer> keyNum = new ArrayList<>(Arrays.asList(1,2));
        // 运算符和界符
        List<String> symbolList = new ArrayList<>(Arrays.asList("+","-"));
        // 运算符和界符的数
        List<Integer> symbolNum = new ArrayList<>(Arrays.asList(10,11));

        // 从文件取出的字符
        String letter;
        // 将字符转为单词
        String words;

        String test ="int main() { int i,j; String a,b;} 123 ccd";

        Parser parser = new Parser();
        parser.analysis(test,keyList);

    }
}

package parser;

import java.util.List;

public class Parser {

    public void analysis(String test,List<String> keyList){
        System.out.println("test:" + test);
        int length = test.length();
        System.out.println("length:" + length);
        // 字符类型
        for(int num=0;num<length;){
            char ch = test.charAt(num);
            System.out.println("ch:" + ch);
            int typeword = typeword(ch);
//            System.out.println("typeword:" + typeword);
            String addword=Character.toString(ch);
            String[] rs;
            switch (typeword){
                case 1:
                    rs= number(test,addword,num,keyList);

                    addword = rs[0];
                    num = Integer.parseInt(rs[1]);
                    System.out.println("<"+addword+",1,int"+">");
                    break;
                case 2:
                    rs= identifier(test,addword,num,keyList);
                    addword = rs[0];
                    num = Integer.parseInt(rs[1]);
                    System.out.println("<"+addword+",2,String"+">");
                    break;
                case 3:
                    rs= symbol(test,addword,num);
                    addword = rs[0];
                    num = Integer.parseInt(rs[1]);
                    System.out.println("<"+addword+",3,symbol"+">");
                    break;
                default:
                    num++;
                    break;
            }
        }
    }

    public int typeword(char str) {
        if (Character.isDigit(str)) {
            return 1;
        }
        if (Character.isLetter(str)) {
            return 2;
        }
        if (Character.toString(str).equals("+") || Character.toString(str).equals("-")) {
            return 3;
        }
        return 0;
    }


    public String[] identifier(String letter, String s, int n, List<String> keyList) {
        int j = n + 1;
        boolean flag = true;

        while (flag) {
            if (j >= letter.length()) {
                break;
            }
            if (isNumeric(letter.charAt(j)) || Character.isLetter(letter.charAt(j))) {
                s += letter.charAt(j);
                if (isKeyword(keyList, s)) {
                    n = ++j;
                    return new String[]{s, String.valueOf(n)};
                }
                j++;
            } else {
                flag = false;
            }
        }
        n = j;
        return new String[]{s, String.valueOf(n)};
    }

    public String[] symbol(String letter, String s, int n) {
        int j = n + 1;
        boolean flag = true;

        while (flag) {
            if (Character.toString(letter.charAt(j)).equals("+") || Character.toString(letter.charAt(j)).equals("-")) {
                s += letter.charAt(j);
                j++;
            } else {
                flag = false;
            }
        }
        n = j;
        return new String[]{s, String.valueOf(n)};
    }

    public String[] number(String letter, String s, int n, List<String> keyList) {
        int j = n + 1;
        boolean flag = true;

        while (flag) {
            if (isNumeric(letter.charAt(j))) {
                s += letter.charAt(j);
                j++;
            } else {
                flag = false;
            }
        }
        n = j;
        return new String[]{s, String.valueOf(n)};
    }

    public static boolean isKeyword(List<String> keyList, String str) {
        try {
            return keyList.contains(str);
        } catch (Exception e) {
            return false;
        }
    }


    public static boolean isNumeric(char str) {
        try {
            Double.parseDouble(Character.toString(str));
            return true;
        } catch (Exception e) {
            return false;
        }
    }
}

测试结果：