Blocks the current Thread (<code>Thread.currentThread()</code>) until the receiver finishes its execution and dies.
@throws InterruptedException if <code>interrupt()</code> was called for the receiver while it was in the <code>join()</code> call
@see Object#notifyAll
@see java.lang.ThreadDeath
join方法的注释上写着：阻塞当前线程，直到收到结束执行或者死亡。当接收者的interrupt方法被调用，并且它被调用了join方法的时候，就会抛出InteruptedException。
举个例子：线程A的run方法中调用了线程B的join，此时线程A处于阻塞状态，直到线程B执行完毕或者死亡的时候，线程A才会继续执行。如果此时线程A处于阻塞状态，而线程B调用线程A的interrupt的时候，就会抛出InterruptedException。
下面举两个例子
示例1：
有两个线程A，B，在A的run方法中，会调用ThreadB.join，也就是说，在ThreadA启动之后，打印出来"ThreadA Started"之后，就会被线程B阻塞。然后线程B开始执行，打印出来"ThreadB started"之后，会休眠5S，之后再打印出"ThreadB Sleep End"，之后线程B执行结束，于是线程A阻塞解除，打印出"ThreadA End"。
public class Test {
public static void main(String[] args) {
ThreadB threadB = new ThreadB();
ThreadA threadA = new ThreadA(threadB);
threadA.start();
threadB.start();
}
private static class ThreadA extends Thread {
ThreadB joinThread;
ThreadA(ThreadB threadB) {
joinThread = threadB;
}
@Override
public void run() {
super.run();
System.out.println("ThreadA Started");
try {
joinThread.join();
} catch (InterruptedException e) {
}
System.out.println("ThreadA End");
}
}
private static class ThreadB extends Thread {
@Override
public void run() {
super.run();
System.out.println("ThreadB started");
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("ThreadB Sleep End");
}
}
}
运行结果：
示例2
和上例不一样的地方是，在ThreadB的Run方法中，Sleep完后，调用ThreadA.interrupt，试一下官方文档上注释对不对。
public class Test {
public static void main(String[] args) {
ThreadB threadB = new ThreadB();
ThreadA threadA = new ThreadA(threadB);
threadB.setThreadA(threadA);
threadA.start();
threadB.start();
}
private static class ThreadA extends Thread {
ThreadB joinThread;
ThreadA(ThreadB threadB) {
joinThread = threadB;
}
@Override
public void run() {
super.run();
System.out.println("ThreadA Started");
try {
joinThread.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("ThreadA End");
}
}
private static class ThreadB extends Thread {
ThreadA threadA;
public void setThreadA(ThreadA threadA) {
this.threadA = threadA;
}
@Override
public void run() {
super.run();
System.out.println("ThreadB started");
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("ThreadB Call ThreadA.interrupt");
threadA.interrupt();
System.out.println("ThreadB Sleep End");
}
}
}
运行结果：
打印出InterruptedException
