键盘录入一个字符串，统计字符串中每个字符串出现的次数（基础）（练习）

package com.HashMap练习01;

import java.util.HashMap;
import java.util.Scanner;
import java.util.Set;

public class main {
    public static void main(String[] args) {
        HashMap<Character,Integer> hm = new HashMap<Character,Integer>();
        //可以使用TreeMap，元素有序
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入一个字符串：");
        String s = scanner.nextLine();
        for (int i = 0; i < s.length(); i++) {
            char key = s.charAt(i);
            Integer value = hm.get(key);
            if (value == null){
                hm.put(key,1);
            }else{
                value++;
                hm.put(key,value);
            }
        }
        StringBuilder stringBuilder = new StringBuilder();
        Set<Character> keySet = hm.keySet();
        for (Character key:keySet) {
            Integer value = hm.get(key);
            stringBuilder.append(key).append("(").append(value).append(")");
        }
        System.out.println(stringBuilder);
    }
}