CountDownLatch

翻译：

倒计时锁存器，，，，count计数，down停止，Latch锁

解释：

允许一个或多个线程等待，直到在其他线程中执行的一组操作完成的同步辅助
不懂？
就是，正常情况下，多线程是同时处于就绪状态，但是，使用了之后，我【线程一】先跑，你们在外面候着

方法

在这里插入图片描述

使用

简单使用

public static void main(String[] args) throws InterruptedException {CountDownLatch countDownLatch = new CountDownLatch(10);for (int i = 0; i < 10; i++) {int finalI = i;new Thread(()->{System.out.println(finalI);countDownLatch.countDown();}).start();}countDownLatch.await();System.out.println("结束了");
}

在线程里使用，每次减少 1
await后面的进程需要等到上面的进程执行完毕，才可以执行

问题？

如何使用CountDownLatch使得角色裁判，喊完各就位预备后，发枪，这个两个动作后，运动员才开始跑

需要使用callable接口，而不是runnable接口

复杂使用

裁判类【Judge】

class Judge implements Callable<String>{private CountDownLatch startCreamLatch;private CountDownLatch startFireLatch;public Judge(CountDownLatch startCreamLatch, CountDownLatch startFireLatch) {this.startCreamLatch = startCreamLatch;this.startFireLatch = startFireLatch;}@Overridepublic String call() throws Exception {scream();this.startCreamLatch.countDown();this.startCreamLatch.await();fire();this.startFireLatch.countDown();this.startFireLatch.await();return "裁判发枪成功";}public void scream (){System.out.println("裁判喊：各就位");}public void fire(){System.out.println("开枪");}
}

定义了scream的CountDownLatch 和 fire的 CountDownLatch
在主类中分别设置倒计时为1，每次执行完，即可以执行下一个

运动员类【runner】

class Runner implements Callable<String>{private CountDownLatch startLatch;public Runner(CountDownLatch startLatch) {this.startLatch = startLatch;}@Overridepublic String call() throws Exception {this.startLatch.await();run();return Thread.currentThread().getName() + "运动员正在运动";}public void run(){System.out.println(Thread.currentThread().getName()+"运动员跑起来了");}
}

主线程【main】

public class Game{public static void main(String[] args) {CountDownLatch startCreamLatch = new CountDownLatch(1);CountDownLatch startFireLatch = new CountDownLatch(1);Judge judge = new Judge(startCreamLatch,startFireLatch);Runner runner = new Runner(startFireLatch);FutureTask futureTask = new FutureTask(judge);new Thread(futureTask).start();for (int i = 0; i < 8; i++) {FutureTask task = new FutureTask(runner);new Thread(task,"第"+String.valueOf(i)+"运动员").start();}}
}