从头认识java-18.2 主要的线程机制（7）join

这一章节我们来讨论一下join。

1.什么是join？

阻塞当前线程，让.join的线程先做完。然后再继续当前线程

以下是api的解释：

A.join,在API中的解释是,阻塞当前线程B,直到A运行完毕并死掉,再运行B。

2.样例：

package com.ray.ch17;

public class Test {

	public static void main(String[] args) throws InterruptedException {
		System.out.println(Thread.currentThread().getName() + " start");
		SleepThread sleepThread = new SleepThread("sleep");
		Thread.sleep(2000);
		JoinThread joinThread = new JoinThread(sleepThread, "join");
//		joinThread.join();
		System.out.println(Thread.currentThread().getName() + " end");
	}
}

class SleepThread extends Thread {

	public SleepThread(String name) {
		super(name);
		start();
	}

	@Override
	public void run() {
		try {
			for (int i = 0; i < 5; i++) {
				System.out.println(getName() + " SleepThread");
				Thread.sleep(1000);
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}

class JoinThread extends Thread {

	private SleepThread sleepThread;

	public JoinThread(SleepThread sleepThread, String name) {
		super(name);
		this.sleepThread = sleepThread;
		start();
	}

	@Override
	public void run() {
		try {
			System.out.println(getName() + " join start");
			sleepThread.join();
			System.out.println(getName() + " join end");
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}

输出：

main start
sleep SleepThread
sleep SleepThread
sleep SleepThread
main end
join join start
sleep SleepThread
sleep SleepThread
join join end

package com.ray.ch17;

public class Test {

	public static void main(String[] args) throws InterruptedException {
		System.out.println(Thread.currentThread().getName() + " start");
		SleepThread sleepThread = new SleepThread("sleep");
		Thread.sleep(2000);
		JoinThread joinThread = new JoinThread(sleepThread, "join");
		joinThread.join();
		System.out.println(Thread.currentThread().getName() + " end");
	}
}

class SleepThread extends Thread {

	public SleepThread(String name) {
		super(name);
		start();
	}

	@Override
	public void run() {
		try {
			for (int i = 0; i < 5; i++) {
				System.out.println(getName() + " SleepThread");
				Thread.sleep(1000);
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}

class JoinThread extends Thread {

	private SleepThread sleepThread;

	public JoinThread(SleepThread sleepThread, String name) {
		super(name);
		this.sleepThread = sleepThread;
		start();
	}

	@Override
	public void run() {
		try {
			System.out.println(getName() + " join start");
			sleepThread.join();
			System.out.println(getName() + " join end");
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}

输出：

main start
sleep SleepThread
sleep SleepThread
sleep SleepThread
join join start
sleep SleepThread
sleep SleepThread
join join end
main end

上面两个代码的不同主要是体如今joinThread.join();是否被凝视。

对照上面的两个代码的输出，主要不同在于main end 的位置。当joinThread.join();的时候，因为须要先阻塞main方法的线程，先完毕joinThread所在线程，因此main end的位置会出现上面的变化。

还有一方面。我们从sleep和join两个线程输出的文字的位置也能够推导出上面的结论。

总结：这一章节我们简介了一下join。

这一章节就到这里，谢谢。

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