java - 对main线程使用join方法，为什么main线程处于一直阻塞状态？

Question

public class JoinTest {

public static void main(String[] args) throws InterruptedException {
    MyThread3 thread=new MyThread3();
    thread.start();
    //thread.join(1);//将主线程加入到子线程后面，不过如果子线程在1毫秒时间内没执行完，则主线程便不再等待它执行完，进入就绪状态，等待cpu调度
    System.out.println(Thread.currentThread());
    Thread.currentThread().join();
    for(int i=0;i<30;i++){
        System.out.println(Thread.currentThread().getName() + "线程第" + i + "次执行！");
    }
}

}

class MyThread3 extends Thread {

@Override
public void run() {
    
    for (int i = 0; i < 1000; i++) {
        try {
            System.out.println(this.getName() + "线程第" + i + "次执行！");
            Thread.sleep(1);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

}

Answer 1

那你得先知道join函数是干嘛用的啊！我们先来看看文档：

/**
 * Waits for this thread to die.
 *
 * <p> An invocation of this method behaves in exactly the same
 * way as the invocation
 *
 * <blockquote>
 * {@linkplain #join(long) join}{@code (0)}
 * </blockquote>
 *
 * @throws  InterruptedException
 *          if any thread has interrupted the current thread. The
 *          <i>interrupted status</i> of the current thread is
 *          cleared when this exception is thrown.
 */

第一句话就说了Waits for this thread to die，你在主线程上执行"我要等到主线程结束，当前线程才能结束"，这不成死循环了么。