面试人员：用Java的多线程模拟一个赛马，马场上有10匹马，要求他们同时起跑

设计到的Java多线程技术：CountDownLatch或者CyclicBarrier

/**
 * <p>
 * <p>Title:testCountDownLatch.java</p >
 * <p>Description: </p >
 * <p>Date:2020/10/20 14:53</p >
 *
 * @author wsh
 * @version 1.0
 */
public class testCountDownLatch {
    CountDownLatch countDownLatch = new CountDownLatch(1);
    private  void runThread(){
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        for(int i=0;i<10 ;i++){
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            executorService.submit(new Runnable() {
                @Override
                public void run() {
                    try {
                        countDownLatch.await();
                        System.out.println("Thread:"+Thread.currentThread().getName()+",time: "+System.currentTimeMillis());
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                }
            });
        }
        countDownLatch.countDown();
    }

    public static void main(String[] args) {
        testCountDownLatch test = new testCountDownLatch();
        test.runThread();
    }
}

运行结果：

/**
 * <p>
 * <p>Title:CyclicBarrierTest.java</p >
 * <p>Description: 做到10个线程同时start</p >
 * <p>Date:2020/10/20 14:41</p >
 *
 * @author wsh
 * @version 1.0
 */
public class CyclicBarrierTest {

    /**
     * CyclicBarrier 适用再多线程相互等待，直到到达一个屏障点。并且CyclicBarrier是可重用的。
     */
    CyclicBarrier cyclicBarrier = new CyclicBarrier(10);

    private void runThread() {
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 10; i++) {
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            executorService.submit(createThread(i));
        }
    }

    private Thread createThread(int i) {
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    cyclicBarrier.await();
                    System.out.println("Thread:" + Thread.currentThread().getName() + "准备完毕,time:" + System.currentTimeMillis());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
            }
        });
        thread.setName("name" + i);
        return thread;
    }

    public static void main(String[] args) {
        CyclicBarrierTest test = new CyclicBarrierTest();
        test.runThread();
    }
}

运行结果：