线程之join() - 爱码网

传送门：https://www.cnblogs.com/techyc/p/3286678.html(本篇文章部分摘自这里）

线程之join()

join()是Thread类的一个方法。根据jdk文档的定义：

public final void join()throws InterruptedException: Waits for this thread to die.

join()方法的作用，是等待这个线程结束；但显然，这样的定义并不清晰。个人认为"Java 7 Concurrency Cookbook"的定义较为清晰：

 

join() method suspends the execution of the calling thread until the object called finishes its execution.

 

也就是说，t.join()方法阻塞调用此方法的线程(calling thread)，直到线程t完成，此线程再继续；通常用于在main()主线程内，等待其它线程完成再结束main()主线程。例如：

/***************************可不看**********************************/
class MyThread implements Runnable {
	Thread thrd;
	
	MyThread(String name)
	{
		thrd = new Thread(this, name);
		thrd.start();
	}
	
	public void run()
	{
		System.out.println(thrd.getName() + " starting");
		try {
			for(int count = 0; count < 10; count++)
			{
				Thread.sleep(400);
				System.out.println("IN" + thrd.getName() + ", count is " + count);
			}
		}catch(InterruptedException exc)
		{
			System.out.println(thrd.getName() + " interrupted ");
		}
		System.out.println(thrd.getName() + " terminating ");
	}
}
/***************************************************************************/
class UseJoin
{
	public static void main(String []args)
	{
		System.out.println("Main thread starting.");
		
		MyThread mt7 = new MyThread("Child #7");
		MyThread mt8 = new MyThread("Child #8");
		MyThread mt9 = new MyThread("Child #9");
		
		try {
			mt7.thrd.join();
			System.out.println(mt7.thrd.getName()+" joined.");
			mt8.thrd.join();
			System.out.println(mt8.thrd.getName()+" joined.");
			mt9.thrd.join();
			System.out.println(mt9.thrd.getName()+" joined.");
			
		}catch(InterruptedException exc)
		{
			System.out.println("Main thread interrupted.");
		}
		System.out.println("Main thread ending");
	}
}

打印结果：

Main thread starting.
Child #9 starting
Child #8 starting
Child #7 starting
INChild #8, count is 0
INChild #9, count is 0
INChild #7, count is 0
INChild #8, count is 1
INChild #7, count is 1
INChild #9, count is 1
INChild #8, count is 2
INChild #7, count is 2
INChild #9, count is 2
INChild #7, count is 3
INChild #9, count is 3
INChild #8, count is 3
INChild #8, count is 4
INChild #7, count is 4
INChild #9, count is 4
INChild #9, count is 5
INChild #8, count is 5
INChild #7, count is 5
INChild #8, count is 6
INChild #7, count is 6
INChild #9, count is 6
INChild #7, count is 7
INChild #8, count is 7
INChild #9, count is 7
INChild #8, count is 8
INChild #9, count is 8
INChild #7, count is 8
INChild #8, count is 9
INChild #9, count is 9
Child #9 terminating 
INChild #7, count is 9
Child #7 terminating 
Child #8 terminating 
Child #7 joined.
Child #8 joined.
Child #9 joined.
Main thread ending

所以，我觉得这句话就可以解释为什么结果是这个了
线程之join()