1、concurrent包下常用的线程安全的集合

CopyOnWriteArrayList

package com.company.ThreadTest;

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

public class TestJUC_CopyOnWriteArrayList {

    public static void main(String[] args) {

        //并发下ArrayList是不安全的可能会报异常：ConcurrentModificationException
        /**
         * 解决方案：
         * 1、List<String> list = new Vector<>();
         * 2、List<String> list = Collections.synchronizedList(new ArrayList<>());
         * 3、List<String> list = new CopyOnWriteArrayList<>();
         */
        //CopyOnWrite 写入时复制 COW思想：计算机设计领域的一种优化策略
        //多线程调用时避免写入覆盖，写入之前先复制一份
        
        List<String> list = new CopyOnWriteArrayList<>();
        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                list.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(list);
            }).start();
        }

    }
}

结果：

[c316f]
[c316f, 350ba, 6b5a7, c1f25, 3a7b6]
[c316f, 350ba, 6b5a7, c1f25]
[c316f, 350ba, 6b5a7]
[c316f, 350ba, 6b5a7, c1f25, 3a7b6, f7f18]
[c316f, 350ba]
[c316f, 350ba, 6b5a7, c1f25, 3a7b6, f7f18, c4f02]
[c316f, 350ba, 6b5a7, c1f25, 3a7b6, f7f18, c4f02, 8aca3, c9f3c]
[c316f, 350ba, 6b5a7, c1f25, 3a7b6, f7f18, c4f02, 8aca3]
[c316f, 350ba, 6b5a7, c1f25, 3a7b6, f7f18, c4f02, 8aca3, c9f3c, d459e]

CopyOnWriteArraySet

package com.company.ThreadTest;

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

public class TestJUC_CopyOnWriteArraySet {

    public static void main(String[] args) {

        //并发下HashSet是不安全的可能会报异常：ConcurrentModificationException
        /**
         * 解决方案：
         * 1、Set<String> set = Collections.synchronizedSet(new HashSet<>());
         * 2、Set<String> set = new CopyOnWriteArraySet<>();
         */
        Set<String> set = new CopyOnWriteArraySet<>();

        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                set.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(set);
            }).start();

        }

    }
}

结果：

[41cc1, ca30b, d90e0, 480d5, ec67b, f5dfa, c7494]
[41cc1, ca30b, d90e0, 480d5, ec67b, f5dfa, c7494, 6d727]
[41cc1, ca30b, d90e0, 480d5, ec67b, f5dfa, c7494]
[41cc1, ca30b, d90e0, 480d5, ec67b, f5dfa, c7494, 6d727, 8d260]
[41cc1, ca30b, d90e0, 480d5, ec67b, f5dfa, c7494]
[41cc1, ca30b, d90e0, 480d5, ec67b, f5dfa, c7494, 6d727, 8d260]
[41cc1, ca30b, d90e0, 480d5, ec67b, f5dfa, c7494, 6d727, 8d260]
[41cc1, ca30b, d90e0, 480d5, ec67b, f5dfa, c7494, 6d727, 8d260]
[41cc1, ca30b, d90e0, 480d5, ec67b, f5dfa, c7494, 6d727]
[41cc1, ca30b, d90e0, 480d5, ec67b, f5dfa, c7494, 6d727, 8d260, e6dca]

ConcurrentHashMap

package com.company.ThreadTest;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;

public class TestJUC_ConcurrentHashMap {

    public static void main(String[] args) {

        //并发下HashMap是不安全的可能会报异常：ConcurrentModificationException
        /**
         * 解决方案：
         * 1、Map<String,String> map = Collections.synchronizedMap(new HashMap<>());
         * 2、Map<String,String> map = new ConcurrentHashMap<>();
         */
        Map<String,String> map = new ConcurrentHashMap<>();

        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                map.put(Thread.currentThread().getName(),UUID.randomUUID().toString().substring(0,5));
                System.out.println(map);
            }).start();

        }

    }
}

结果：

{Thread-3=72d8c, Thread-4=2d5d0, Thread-5=a2291, Thread-6=c2cca, Thread-2=62441}
{Thread-3=72d8c, Thread-4=2d5d0, Thread-5=a2291, Thread-6=c2cca, Thread-7=1f50f, Thread-2=62441}
{Thread-3=72d8c, Thread-4=2d5d0, Thread-5=a2291, Thread-6=c2cca, Thread-7=1f50f, Thread-8=8fef8, Thread-2=62441}
{Thread-3=72d8c, Thread-4=2d5d0, Thread-5=a2291, Thread-6=c2cca, Thread-7=1f50f, Thread-8=8fef8, Thread-9=db25d, Thread-2=62441}
{Thread-3=72d8c, Thread-4=2d5d0, Thread-5=a2291, Thread-6=c2cca, Thread-7=1f50f, Thread-2=62441}
{Thread-3=72d8c, Thread-4=2d5d0, Thread-5=a2291, Thread-6=c2cca, Thread-7=1f50f, Thread-2=62441}
{Thread-3=72d8c, Thread-4=2d5d0, Thread-5=a2291, Thread-6=c2cca, Thread-2=62441}
{Thread-3=72d8c, Thread-4=2d5d0, Thread-5=a2291, Thread-6=c2cca, Thread-7=1f50f, Thread-8=8fef8, Thread-2=62441}
{Thread-3=72d8c, Thread-4=2d5d0, Thread-5=a2291, Thread-6=c2cca, Thread-7=1f50f, Thread-8=8fef8, Thread-9=db25d, Thread-0=05ea8, Thread-2=62441}
{Thread-3=72d8c, Thread-4=2d5d0, Thread-5=a2291, Thread-6=c2cca, Thread-7=1f50f, Thread-8=8fef8, Thread-9=db25d, Thread-0=05ea8, Thread-1=95c99, Thread-2=62441}