集合类不安全

List

package com.luoKing.unsafe;
 
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
import java.util.Vector;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.TimeUnit;
 
public class listTest {
/*
* 使用 List会出现 ConcurrentModificationException：并发修改异常
* 解决方法
* 1. List<String> list = new CopyOnWriteArrayList<>();
* 2. List<String> list = new Vector<>();
 
* 为什么使用CopyOnWriteArrayList而不使用Vector？
* 应为vector.add方法是同步方法，CopyOnWriteArrayList.add方法中用lock锁达到同步
* 我们知道synchronized运行效率比Lock锁慢
*
 * */
    public static void main(String[] args) {
        List<String> list = new Vector<>();
        for (int i = 1; i <= 10; i++) {
//            try {
//                TimeUnit.SECONDS.sleep(1);
//            } catch (InterruptedException e) {
//                e.printStackTrace();
//            }
            new Thread(()->{
 
                list.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}
 

Set

package com.luoKing.unsafe;
 
import java.util.*;
import java.util.concurrent.CopyOnWriteArraySet;
 
 
/*
* 使用HashSet会出现线程不安全问题 ConcurrentModificationException:
* 解决方法
* 1. Set<Object> set = new CopyOnWriteArraySet<>();
* 2. Set<Object> set = Collections.synchronizedSet(new HashSet<>());
* */
public class SetTest {
    public static void main(String[] args) {
//        HashSet set = new HashSet();
        Set<Object> set = Collections.synchronizedSet(new HashSet<>());
        for (int i = 0; i < 20; i++) {
            new Thread(()->{
                set.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(set);
            }).start();
        }
    }
 
}
 

Map

package com.luoKing.unsafe;
 
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
 
/*
* 单纯的HashMap会有并发问题，ConcurrentModificationException：同步修改异常
*解决方法：
*        Map<String, String> map = new ConcurrentHashMap<>();
* */
 
public class MapTest {
 
    public static void main(String[] args) {
        Map<String, String> map = new ConcurrentHashMap<>();
 
        for (int i = 0; i < 200; i++) {
            new Thread(()->{
                map.put(Thread.currentThread().getName(), UUID.randomUUID().toString().substring(0,5));
                System.out.println(map);
            },String.valueOf(i)).start();
        }
    }
}