java集合中自定义对象出现次数

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package com.zcsj.test;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import java.util.Map.Entry;public class Demo6 {public static void main(String[] args) {Demo d1 = new Demo("1", "a" );Demo d2 = new Demo("2", "b");Demo d3 = new Demo("3", "c");List<Demo> demos = new ArrayList<Demo>();demos.add(d1);demos.add(d2);demos.add(d2);demos.add(d3);demos.add(d3);demos.add(d3);Map<String ,List<Demo>> map = new HashMap<String ,List<Demo>>();for (Demo demo : demos) {if(map.containsKey(demo.id)){map.get(demo.id).add(demo);} else {ArrayList<Demo> temp = new ArrayList();temp.add(demo);map.put(demo.id, temp);}}for (Entry<String, List<Demo>> entry : map.entrySet()) {System.out.println(entry.getKey()+"出现次数："+entry.getValue().size());}}}class Demo {public String id;public String name;public Demo(String id, String name) {this.id = id;this.name = name;}public Demo() {}}

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