慎用java集合中的clear()方法

Love The Way You Lie 2022-05-31 01:58 274阅读 0赞

一、不多说了，直接上代码和结果：

1.代码

package com.xbl.rocketMq.consumer;
    
    import org.bson.Document;
    
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    
    /**
     * Created by lenovo on 2018-02-01.
     */
    public class T {
        public static void main(String[] args) {
            List<Map<String,String>> list = new ArrayList<Map<String,String>>();
            Map<String,String> map = new HashMap<String,String>();
            for(int i=0;i<3;i++){
                map.put(""+i,""+i+100);
                list.add(map);
            }
            System.out.println("list的长度："+list.size());
            System.out.println("list.get(0)："+list.get(0));
            System.out.println("list.get(1)："+list.get(1));
            System.out.println("list.get(2)："+list.get(2));
            
            System.out.println("===============");
            
            System.out.println("开始执行：map.clear()");
            map.clear();
            System.out.println("开始执行：map.put(\"222\",\"222222222\")");
            map.put("222","222222222");//************
            System.out.println("list的长度："+list.size());
            System.out.println("list.get(0)："+list.get(0));
            System.out.println("list.get(1)："+list.get(1));
            System.out.println("list.get(2)："+list.get(2));
            
            System.out.println("--------------------------------");
            
            List<Document> w_c_data = new ArrayList<Document>();
            Document middle = new Document();
            for(int i=0;i<3;i++){
                middle.put("want_content_id",""+i);
                middle.put("want_content_name",""+i);
                w_c_data.add(middle);
            }
            middle.put("111","111111111111");//************
            System.out.println("w_c_data的长度："+w_c_data.size()+"***");
            System.out.println(w_c_data.get(0)+"%%%%");
            System.out.println(w_c_data.get(1)+"%%%%");
            System.out.println(w_c_data.get(2)+"%%%%");
            
            System.out.println("================");
            
            System.out.println("开始执行：middle.clear()");
            middle.clear();//************
            System.out.println("开始执行： middle.put(\"111\",\"111111111111\")");
            middle.put("111","111111111111");
            System.out.println("w_c_data.get(0): " + w_c_data.get(0)+"%%%%");
            System.out.println("w_c_data.get(1): " + w_c_data.get(1)+"%%%%");
            System.out.println("w_c_data.get(2): " + w_c_data.get(2)+"%%%%");
    
        }
    }

2.结果：

list的长度：3
    list.get(0)：{2=2100, 1=1100, 0=0100}
    list.get(1)：{2=2100, 1=1100, 0=0100}
    list.get(2)：{2=2100, 1=1100, 0=0100}
    ===============
    开始执行：map.clear()
    开始执行：map.put("222","222222222")
    list的长度：3
    list.get(0)：{222=222222222}
    list.get(1)：{222=222222222}
    list.get(2)：{222=222222222}
    --------------------------------
    w_c_data的长度：3***
    Document{
       {want_content_id=2, want_content_name=2, 111=111111111111}}%%%%
    Document{
       {want_content_id=2, want_content_name=2, 111=111111111111}}%%%%
    Document{
       {want_content_id=2, want_content_name=2, 111=111111111111}}%%%%
    ================
    开始执行：middle.clear()
    开始执行： middle.put("111","111111111111")
    w_c_data.get(0): Document{
       {111=111111111111}}%%%%
    w_c_data.get(1): Document{
       {111=111111111111}}%%%%
    w_c_data.get(2): Document{
       {111=111111111111}}%%%%
    
    Process finished with exit code 0