Day0202____集合复习

HashMap  无序

linkedHashMap 进入顺序排序

TreeMap value排序

 

package com_01_testfan_02_basic;

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

public class Day01_06_作业2 {
    
    
    public static void main(String[] args) {
        String testString="2342a2sfghgyu56asdasdaddddd";
        //0 //length()-1
        //char char_str =testString.charAt(testString.length()-1);
        //Map<String, Integer> mapcount = new LinkedHashMap<String, Integer>();
        //Map<String, Integer> mapcount = new TreeMap<String, Integer>();
        Map<String, Integer> mapcount = new HashMap<String, Integer>();
        
        for (int i = 0; i < testString.length(); i++) {
            //System.out.println(testString.charAt(i));
            String key =String.valueOf(testString.charAt(i));
            //如果map 不存在 value 1
            if(!mapcount.containsKey(key)) {
                mapcount.put(key, 1);
            }else {
            //如果存在
                int value = mapcount.get(key);
                value +=1;
                mapcount.put(key, value);
            }
        }
        
        Set<String> keySet =mapcount.keySet();
        for (String key : keySet) {
            System.out.println(key +" "+mapcount.get(key));
        }
        
        //System.out.println(char_str);
    }

}