join方法的使用

join方法是Thread类直接提供的，线程A调用线程B的join方法后，会被阻塞，等待B完成。
如果此时其他线程调用了线程A的interrupt()方法，线程A会抛出InterruptException异常

 public static void main(String[] args) throws InterruptedException {
        Thread threadOne=new Thread(()->{
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            System.out.println("child threadOne over!");
        });



        Thread threadtwo=new Thread(()->{
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            System.out.println("child threadTwo over!");
        });


        System.out.println("time:"+System.currentTimeMillis());
        threadOne.start();
        threadtwo.start();
        System.out.println("wait all child thread over!");
        threadOne.join();
        threadtwo.join();
        System.out.println("time:"+System.currentTimeMillis());
        
    }

输出

time:1563012587684
wait all child thread over!
child threadTwo over!
child threadOne over!
time:1563012588687

这里main线程调用了threadOne的join方法 ，就会进行阻塞 等待threadOne执行完毕之后返回，只有threadOne执行完毕之后，threadOne.join()方法才会返回。
返回之后在main线程调用threadtwo.join()，等待threadTwo完成。
这里，threadOne和ThreadTwo都只执行1秒，所以最终的运行结果就是main线程阻塞了1秒。

修改ThreadOne和ThreadTwo的sleep时间为5秒，3秒，最终需要等待的时间是5秒

time:1563012942271
wait all child thread over!
child threadOne over!
child threadTwo over!
time:1563012947272

改成

   System.out.println("time:"+System.currentTimeMillis());
        threadOne.start();
        threadtwo.start();
        System.out.println("wait threadOne child thread over!");
        threadOne.join();
        System.out.println("wait threadtwo child thread over!");
        threadtwo.join();
        System.out.println("time:"+System.currentTimeMillis());

输出

time:1563013009495
wait threadOne child thread over!
child threadOne over!
wait threadtwo child thread over!
child threadTwo over!
time:1563013014500

如果在join的时候，有其他线程调用了该线程的interrupter方法，此时会在该线程调用join()所在的行抛出InterruptedException 并立即返回。

//获取主线程
        Thread mainThread=Thread.currentThread();

        new Thread(()->{
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            mainThread.interrupt();
            System.out.println("Interrupted main!");
        }).start();

输出如下

time:1563013331167
wait threadOne child thread over!
Interrupted main!
Exception in thread "main" java.lang.InterruptedException
	at java.lang.Object.wait(Native Method)
	at java.lang.Thread.join(Thread.java:1252)
	at java.lang.Thread.join(Thread.java:1326)
	at JoinDemo.main(JoinDemo.java:52)
child threadOne over!
child threadTwo over!

标签：join,threadOne,Thread,over,使用,System,child,方法
来源： https://blog.csdn.net/qq_20009015/article/details/95775317