CountDownLatch

        应用场景：1.多线程任务汇总。2.多线程任务阻塞住，等待发令枪响，一起执行。

  减法计数器

        每次有线程调用，数量-1，当计数器归零，countDownLatch.await()就会被唤醒向下执行。

import java.util.concurrent.CountDownLatch;// 计数器
public class CountDownLatchDemo {public static void main(String[] args) throws InterruptedException {//总数是6  必须要执行任务的时候再使用CountDownLatch countDownLatch = new CountDownLatch(6);for (int i = 0; i < 6; i++) {new Thread(()->{System.out.println(Thread.currentThread().getName() + " Go out");countDownLatch.countDown();//数量-1},String.valueOf(i)).start();}countDownLatch.await();System.out.println("Close Door");}}

原理：

        countDownLatch.countDown(); //数量-1

        countDownLatch.await();//等待计数器归零，然后再往下执行

        每次线程调用countDown()数量-1，假设计数器变成0，countDownLatch.await()就会被唤醒，继续执行！

CyclicBarrier

        应用场景：比如LOL类游戏，满10人一组，开始游戏。

        加法计算器

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;public class CyclicBarrierDemo {public static void main(String[] args) {//集齐七颗龙珠召唤神龙CyclicBarrier cyclicBarrier = new CyclicBarrier(7,()->{System.out.println("召唤神龙成功！");});for (int i = 1; i <= 7; i++) {final int temp = i;new Thread(()->{System.out.println(Thread.currentThread().getName() + "收集了第" + temp + "颗龙珠");try {cyclicBarrier.await();} catch (InterruptedException e) {e.printStackTrace();} catch (BrokenBarrierException e) {e.printStackTrace();}}).start();}}
}

Semaphore

        Semaphore：信号量

        抢车位(6辆车，3个停车位)

import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;public class SemaphoreDemo {public static void main(String[] args) {//线程数量 比作 停车位Semaphore semaphore = new Semaphore(3);for (int i = 1; i <= 6; i++) {new Thread(()->{//acquire() 得到try {semaphore.acquire();System.out.println(Thread.currentThread().getName() + "抢到车位");TimeUnit.SECONDS.sleep(2);System.out.println(Thread.currentThread().getName() + "离开车位");} catch (InterruptedException e) {e.printStackTrace();}finally {//release() 释放semaphore.release();}},String.valueOf(i)).start();}}
}

原理：

        semaphore.acquire(); //获得，假设已经满了，等待，等待被释放为止！

        semaphore.release();//释放，会将当前的信号量释放，然后唤醒等待线程！

作用:

        多个共享资源互斥使用！并发限流，控制最大线程数！