juc包

java.util.concurrent，并发包

1. CopyOnWriteArrayList是线程安全的。

package util;

import java.util.concurrent.CopyOnWriteArrayList;

public class TestCopyOnWriteArrayList {
    public static void main(String[] args) {
        CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<String>();
        for(int i = 0; i< 10000;i++){
            new Thread(()->{
                list.add(Thread.currentThread().getName());
            });
        }
        try {
            Thread.sleep(3000);//这里是为了防止主线程先执行完，而子线程还没有创建完，获取的list.size()可能不准，所以让主线程休眠，确保子线程执行完。
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

2. java.util.concurrent.locks.Lock
   synchronized是隐式锁，Lock是显示锁。ReentrantLock类是可重入锁，实现了Lock,不要忘记释放锁。

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import java.util.concurrent.locks.ReentrantLock;

public class TestLock implements Runnable {
    private static int ticketNum = 3;
    private boolean flag = true;

    //定义Lock锁
    private final ReentrantLock lock = new ReentrantLock();

    @Override
    public void run() {

        while (flag) {

            try {
                lock.lock();//加锁
                if (ticketNum > 0) {
                    Thread.sleep(100);
                    System.out.println(Thread.currentThread().getName() + "获得票" + ticketNum--);
                } else {
                    flag = false;
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                lock.unlock(); //释放锁
            }

        }

    }

    public static void main(String[] args) {
        TestLock lock = new TestLock();

        Thread thread = new Thread(lock);
        Thread thread1 = new Thread(lock);
        Thread thread2 = new Thread(lock);
        thread.start();
        thread1.start();
        thread2.start();


    }
}