如何让线程A,B,C顺序执行

有时候我们会遇到这样的场景，就是在某个线程执行完后，才能执行其它线程，基于这个那么如何让多个线程顺序执行呢？

现在有A,B,C三个线程，那么怎样让A线程执行完后B执行最后C执行。

     三个线程类如下：

   

class ThreadA implements Runnable{
	@Override
	public void run() {
		// TODO Auto-generated method stub
		System.out.println("ThreadA "+Thread.currentThread().getName()+" Start....");
	}
}

class ThreadB implements Runnable{
	@Override
	public void run() {
		// TODO Auto-generated method stub
	   System.out.println("ThreadB "+Thread.currentThread().getName()+" Start....");	
	}
}

class ThreadC implements Runnable{
	@Override
	public void run() {
		// TODO Auto-generated method stub
		System.out.println("ThreadC "+Thread.currentThread().getName()+" Start....");
	}
}

 

• 使用join

         join作用是：如果某个线程调用join方法，优先执行完该线程，才能够执行其它线程。

         调用如下：

        Thread a = new Thread(new ThreadA(),"A");
	Thread b = new Thread(new ThreadB(),"B");
	Thread c = new Thread(new ThreadC(),"C");
        a.start();
	a.join();
	b.start();
	b.join();
	c.start();
	c.join();	

       输出：ThreadA A Start....     ThreadB B Start....     ThreadC C Start....

• 使用单线程池

          调用如下：

          

                Thread a = new Thread(new ThreadA(),"A");
		Thread b = new Thread(new ThreadB(),"B");
		Thread c = new Thread(new ThreadC(),"C");
		
		ExecutorService singlePool = Executors.newSingleThreadExecutor();
		singlePool.submit(a);
		singlePool.submit(b);
		singlePool.submit(c);
		singlePool.shutdown();  //要关闭，要不然会一直等待线程

       输出：ThreadA pool-1-thread-1 Start....   ThreadB pool-1-thread-1 Start....    ThreadC pool-1-thread-1 Start....

• 使用CountDownLatch

可以把CountDownLatch看作是一个计数器，如果调用其await()方法，那么此对象就会一直处于等待状态，直到countDown为0，才会继续执行下去。

class Worker implements Runnable{
	CountDownLatch c1;
	CountDownLatch c2;
	
	public Worker(CountDownLatch c1,CountDownLatch c2) {
		this.c1 = c1;
		this.c2 = c2;
	}
	
	
	@Override
	public void run() {
		// TODO Auto-generated method stub
		try {
			this.c1.await();
			System.out.println("Thread "+Thread.currentThread().getName()+" Start....");
			this.c2.countDown();
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
}

调用如下：

  

                CountDownLatch c1 = new CountDownLatch(0);
		CountDownLatch c2 = new CountDownLatch(1);
		CountDownLatch c3 = new CountDownLatch(1);
		Thread a = new Thread(new Worker(c1,c2),"A");
		Thread b = new Thread(new Worker(c2,c3),"B");
		Thread c = new Thread(new Worker(c3,c3),"C");
		a.start();
		b.start();
		c.start();

   输出：Thread A Start....    Thread B Start....    Thread C Start....