@toc

1 ArrayList线程不安全

1.1 ArrayList线程不安全演示

直接开启30个线程往集合中添加数据

package com.atguigu.lock;

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CopyOnWriteArraySet;

/**
 * List集合线程不安全
 */
public class ThreadDemo4 {
    public static void main(String[] args) {
        //创建ArrayList
        List<String> list = new ArrayList<>();

        for (int i = 0; i <30 ; i++) {
            new Thread(()->{
                //向集合添加内容
                list.add(UUID.randomUUID().toString().substring(0,8));
                //从集合获取内容
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}

可以看到，引发了线程安全问题

1.2 解决ArrayList线程不安全

1.2.1 解决方案-Vector

public class ThreadDemo4 {
    public static void main(String[] args) {
        //创建ArrayList
        List<String> list = new Vector<>();

        for (int i = 0; i <30 ; i++) {
            new Thread(()->{
                //向集合添加内容
                list.add(UUID.randomUUID().toString().substring(0,8));
                //从集合获取内容
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}

1.2.2 解决方案-Collections

public class ThreadDemo4 {
    public static void main(String[] args) {
        //创建ArrayList
        List<String> list =Collections.synchronizedList(new ArrayList<>());

        for (int i = 0; i <30 ; i++) {
            new Thread(()->{
                //向集合添加内容
                list.add(UUID.randomUUID().toString().substring(0,8));
                //从集合获取内容
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}

1.2.3 解决方案:CopyOnWriteArrayList(写时复制技术 推荐)

```java
public class ThreadDemo4 {
    public static void main(String[] args) {
        //创建ArrayList
        List<String> list =new CopyOnWriteArrayList<>();

        for (int i = 0; i <30 ; i++) {
            new Thread(()->{
                //向集合添加内容
                list.add(UUID.randomUUID().toString().substring(0,8));
                //从集合获取内容
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}

2 HashSet线程不安全

2.1 HashSet线程不安全演示

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CopyOnWriteArraySet;

/**
 * List集合线程不安全
 */
public class ThreadDemo4 {
    public static void main(String[] args) {
       //演示HashSet线程不安全
        Set<String> set = new HashSet<>();
        //解决方案:CopyOnWriteArraySet
//        Set<String> set = new CopyOnWriteArraySet<>();
        for (int i = 0; i <30 ; i++) {
            new Thread(()->{
                //向集合添加内容
                set.add(UUID.randomUUID().toString().substring(0,8));
                //从集合获取内容
                System.out.println(set);
            },String.valueOf(i)).start();
        }
    }
}

2.2 解决方案：CopyOnWriteArraySet

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CopyOnWriteArraySet;

/**
 * List集合线程不安全
 */
public class ThreadDemo4 {
    public static void main(String[] args) {
       //演示HashSet线程不安全
      //  Set<String> set = new HashSet<>();
        //解决方案:CopyOnWriteArraySet
        Set<String> set = new CopyOnWriteArraySet<>();
        for (int i = 0; i <30 ; i++) {
            new Thread(()->{
                //向集合添加内容
                set.add(UUID.randomUUID().toString().substring(0,8));
                //从集合获取内容
                System.out.println(set);
            },String.valueOf(i)).start();
        }
    }
}

3、HashMap线程不安全

3.1 HashMap线程不安全演示

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CopyOnWriteArraySet;

/**
 * List集合线程不安全
 */
public class ThreadDemo4 {
    public static void main(String[] args) {
        //演示HashMap
        Map<String,String> map = new HashMap<>();
        for (int i = 0; i <30 ; i++) {
            String key=String.valueOf(i);
            new Thread(()->{
                //向集合添加内容
                map.put(key,UUID.randomUUID().toString().substring(0,8));
                //从集合获取内容
                System.out.println(map);
            },String.valueOf(i)).start();
        }
    }
}

3.2 解决方案：ConcurrentHashMap

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CopyOnWriteArraySet;

/**
 * List集合线程不安全
 */
public class ThreadDemo4 {
    public static void main(String[] args) {
        //演示HashMap
        Map<String,String> map = new ConcurrentHashMap<>();
        for (int i = 0; i <30 ; i++) {
            String key=String.valueOf(i);
            new Thread(()->{
                //向集合添加内容
                map.put(key,UUID.randomUUID().toString().substring(0,8));
                //从集合获取内容
                System.out.println(map);
            },String.valueOf(i)).start();
        }
    }
}