主线程等待子线程结束后再运行

1.join

将子线程插入到主线程中，主线程和子线程合并为顺序执行的线程

public class Test {
    public static void main(String[] args) throws Exception {
        List<Thread> list = new ArrayList<Thread>();
        for(int i=0; i<10; i++){
            Thread thread = new Thread(new Runnable(){
                public void run(){
                    try {
                        Thread.sleep(5*1000);
                    } catch (Exception e) {
                        // TODO: handle exception
                    }
                    System.out.println("子线程执行完毕!");
                }
            });
            list.add(thread);
            thread.start();
        }
        for(Thread thread : list){
            thread.join();
        }
        System.out.println("主线程执行完毕!");
    }
}

2.CountDownLatch

public class Test {
    public static void main(String[] args) throws Exception {
        List<Thread> list = new ArrayList<Thread>();
        final CountDownLatch latch = new CountDownLatch(10);
        for(int i=0; i<10; i++){
            Thread thread = new Thread(new Runnable(){
                public void run(){
                    try {
                        Thread.sleep(5*1000);
                    } catch (Exception e) {
                        // TODO: handle exception
                    }
                    latch.countDown();
                    System.out.println("子线程执行完毕!");
                }
            });
            list.add(thread);
            thread.start();
        }
        
        latch.await();
        System.out.println("主线程执行完毕!");
    }
}

3.CyclicBarrier

public class Test {
    public static void main(String[] args) throws Exception {
        List<Thread> list = new ArrayList<Thread>();
        final CyclicBarrier cyclic = new CyclicBarrier(10);
        for(int i=0; i<10; i++){
            new Thread(new Runnable(){
                public void run(){
                    try {
                        Thread.sleep(5*1000);
                    } catch (Exception e) {
                        // TODO: handle exception
                    }
                    try {
                        cyclic.await();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    } catch (BrokenBarrierException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    System.out.println("子线程执行完毕!");
                }
            }).start();;
        }
        
        cyclic.await();
        System.out.println("主线程执行完毕!");
    }
}