java - join() 方法在多线程中如何工作

Question

根据我对 join() 方法的理解，它允许一个线程等待另一个线程完成。

然后，根据我的代码:一旦线程(t0)结束，线程(t3)就应该启动，但这不会发生

public class Threaded extends Thread {

     @Override
     public void run() {

      for (int i=0; i<5; i++) {

           System.out.println(Thread.currentThread().getName() + ": " + i);

       }

       }

}

public class Demo {

    public static void main(String[] args) throws InterruptedException {

        Thread main = Thread.currentThread();

        Threaded t0 = new Threaded();
        Threaded t1 = new Threaded();
        Threaded t2 = new Threaded();
        Threaded t3= new Threaded();

        t0.start();
        t1.start();
        t2.start();

        t0.join();

        t3.start();

    }

}

输出为

main 5  
Thread-1: 0  
Thread-2: 0  
Thread-0: 0  
Thread-2: 1  
Thread-2: 2  
Thread-1: 1  
Thread-2: 3  
Thread-2: 4  
Thread-0: 1  
Thread-0: 2  
Thread-0: 3  
Thread-0: 4  
Thread-1: 2  
Thread-1: 3  
Thread-1: 4  
Thread-3: 0  
Thread-3: 1  
Thread-3: 2  
Thread-3: 3  
Thread-3: 4

在此输出中，Thread-3 在 Thread-0、Thread-1 和 Thread-2 结束后启动。 但是，根据我的说法，Thread-3 会在 Thread-0 结束后立即启动。

Answer 1

Thread-3 starts as soon as the Thread-0 ends.

Thread-0 完成后，Thread-3 即可运行。但这并不意味着立即安排。可能同时有 3 个可运行线程，并且无法预测哪个线程先打印。