public static void main(String[] args) {

    //定义一个CountDownLatch

    CountDownLatch countDownLatch = new CountDownLatch(3);

    // 主线程等待另外三个线程执行完成后再执行

    new Thread(() -> {

        try {

            System.out.println("开始执行01");

            Thread.sleep(3000);

            System.out.println("执行完成01");

            countDownLatch.countDown();

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

    }).start();

    new Thread(() -> {

        try {

            System.out.println("开始执行02");

            Thread.sleep(3000);

            System.out.println("执行完成02");

            countDownLatch.countDown();

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

    }).start();

    new Thread(() -> {

        try {

            System.out.println("开始执行03");

            Thread.sleep(3000);

            System.out.println("执行完成03");

            countDownLatch.countDown();

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

    }).start();

    try {

        System.out.println("等待3个线程执行完毕。。。");

        countDownLatch.await();

        System.out.println("主线程开始执行");

    } catch (InterruptedException e) {

        e.printStackTrace();

    }

}

public static void main(String[] args) {

    CyclicBarrier cyclicBarrier = new CyclicBarrier(3);

    // 三个线程互相等待await执行完成后继续执行

    new Thread(() -> {

        try {

            System.out.println("开始执行01");

            Thread.sleep(3000);

            System.out.println("执行完成01");

            cyclicBarrier.await();

        } catch (InterruptedException e) {

            e.printStackTrace();

        } catch (BrokenBarrierException e) {

            e.printStackTrace();

        }

        System.out.println(Thread.currentThread().getName()+"所有线程执行完毕，继续处理其他任务...");

    }).start();

    new Thread(() -> {

        try {

            System.out.println("开始执行02");

            Thread.sleep(3000);

            System.out.println("执行完成02");

            cyclicBarrier.await();

        } catch (InterruptedException e) {

            e.printStackTrace();

        } catch (BrokenBarrierException e) {

            e.printStackTrace();

        }

        System.out.println(Thread.currentThread().getName()+"所有线程执行完毕，继续处理其他任务...");

    }).start();

    new Thread(() -> {

        try {

            System.out.println("开始执行03");

            Thread.sleep(3000);

            System.out.println("执行完成03");

            cyclicBarrier.await();

        } catch (InterruptedException e) {

            e.printStackTrace();

        } catch (BrokenBarrierException e) {

            e.printStackTrace();

        }

        System.out.println(Thread.currentThread().getName()+"所有线程执行完毕，继续处理其他任务...");

    }).start();

}

public class Test {

    public static void main(String[] args) {

        int N = 8;            //工人数

        Semaphore semaphore = new Semaphore(5); //机器数目

        for(int i=0;i<N;i++)

            new Worker(i,semaphore).start();

    }

    static class Worker extends Thread{

        private int num;

        private Semaphore semaphore;

        public Worker(int num,Semaphore semaphore){

            this.num = num;

            this.semaphore = semaphore;

        }

        @Override

        public void run() {

            try {

                semaphore.acquire();

                System.out.println("工人"+this.num+"占用一个机器在生产...");

                Thread.sleep(2000);

                System.out.println("工人"+this.num+"释放出机器");

                semaphore.release();

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

        }

    }

}