Java 简明教程

Java - Joining Threads

创建 Thread 对象后，可以通过调用 start() method 开始该对象，这会执行对 run() method 的调用。在运行多个线程的情况下，我们可以阻止当前线程，直到另一个线程终止为止。

Joining Threads in Java

在 Java 中联接线程指的是在另一个线程完成执行之前等待（或阻塞）线程。 Thread class 的 join() 方法用于此目的。

Syntax

以下是 join() 方法的简单语法 -

void join();

Overloaded Thread.join() Methods

以下是三个重载的 join() 方法 -

  1. join() − 当前线程在第二个线程上调用此方法，导致当前线程阻塞，直到第二个线程终止。

  2. join(long millisec) − 当前线程在第二个线程上调用此方法，导致当前线程阻塞，直到第二个线程终止或经过指定数量的毫秒。

  3. join(long millisec, int nanos) − 当前线程在第二个线程上调用此方法，导致当前线程阻塞，直到第二个线程终止或经过指定的毫秒数 + 纳秒数。

Example of Joining Threads in Java

在此示例中，我们将通过实现 Runnable 接口来创建一个类 RunnableDemo。RunnableDemo 类有 run() 方法实现。在主类 TestThread 中，我们创建了 RunnableDemo 对象，并利用这些对象创建了两个 Thread 对象。在每个线程对象上调用 Thread.start() 方法时，线程开始处理，并执行程序。使用 join() 方法，我们阻塞了当前线程，以确保只有在一个线程完成后，才开始下一个线程。

package com.tutorialspoint;

class RunnableDemo implements Runnable {
   RunnableDemo( ) {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: New");
   }

   public void run() {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Running");
      for(int i = 4; i > 0; i--) {
         System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i);
      }
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Dead");
   }
}

public class TestThread {
   public static void main(String args[]) throws InterruptedException {
      Thread t1 = new Thread( new RunnableDemo(), "Thread-1");
      Thread t2 = new Thread( new RunnableDemo(), "Thread-2");
      Thread t3 = new Thread( new RunnableDemo(), "Thread-3");
      // start t1 thread and join main thread
      t1.start();
      t1.join();
      // t2 will start when t1 is dead
      t2.start();
      t2.join();
      // t3 will start when t2 is dead
      t3.start();
   }
}
Thread: Thread-1, State: New
Thread: Thread-2, State: New
Thread: Thread-1, State: Running
Thread: Thread-1, 4
Thread: Thread-1, 3
Thread: Thread-1, 2
Thread: Thread-1, 1
Thread: Thread-1, State: Dead
Thread: Thread-2, State: Running
Thread: Thread-2, 4
Thread: Thread-2, 3
Thread: Thread-2, 2
Thread: Thread-2, 1
Thread: Thread-2, State: Dead

More Example of Joining Threads in Java

Example 1

在此示例中，我们将通过实现 Runnable 接口来创建一个类 RunnableDemo。RunnableDemo 类有 run() 方法实现。在主类 TestThread 中，我们创建了 RunnableDemo 对象，并利用这些对象创建了两个 Thread 对象。在每个线程对象上调用 Thread.start() 方法时，线程开始处理，并执行程序。使用 join(long millisec) 方法，我们阻塞当前线程 200 毫秒，以确保只有在一个线程完成后或经过 200 毫秒延迟后，才开始下一个线程。

package com.tutorialspoint;

class RunnableDemo implements Runnable {
   RunnableDemo( ) {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: New");
   }

   public void run() {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Running");
      for(int i = 4; i > 0; i--) {
         try {
            Thread.sleep(50);
         } catch (InterruptedException e) {
            // TODO Auto-generated catch block
         e.printStackTrace();
         }
         System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i);
      }
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Dead");
   }
}

public class TestThread {
   public static void main(String args[]) throws InterruptedException {
      Thread t1 = new Thread( new RunnableDemo(), "Thread-1");
      Thread t2 = new Thread( new RunnableDemo(), "Thread-2");
      Thread t3 = new Thread( new RunnableDemo(), "Thread-3");
      // start t1 thread and join main thread
      t1.start();
      t1.join(200);
      // t2 will start when t1 is dead or 200 ms is elapsed
      t2.start();
      t2.join(200);
      // t3 will start when t2 is dead or 200 ms is elapsed
      t3.start();
   }
}
Thread: main, State: New
Thread: main, State: New
Thread: main, State: New
Thread: Thread-1, State: Running
Thread: Thread-1, 4
Thread: Thread-1, 3
Thread: Thread-1, 2
Thread: Thread-2, State: Running
Thread: Thread-1, 1
Thread: Thread-1, State: Dead
Thread: Thread-2, 4
Thread: Thread-2, 3
Thread: Thread-2, 2
Thread: Thread-3, State: Running
Thread: Thread-2, 1
Thread: Thread-2, State: Dead
Thread: Thread-3, 4
Thread: Thread-3, 3
Thread: Thread-3, 2
Thread: Thread-3, 1
Thread: Thread-3, State: Dead

Example 2

在此示例中，我们将通过实现 Runnable 接口来创建一个类 RunnableDemo。RunnableDemo 类有 run() 方法实现。在主类 TestThread 中，我们创建了 RunnableDemo 对象，并利用这些对象创建了两个 Thread 对象。在每个线程对象上调用 Thread.start() 方法时，线程开始处理，并执行程序。使用 join(long millisec, long nanoseconds) 方法，我们阻塞当前线程 200 毫秒和 100000 纳秒，以确保只有在一个线程完成后或经过 201 毫秒延迟后，才开始下一个线程。

package com.tutorialspoint;

class RunnableDemo implements Runnable {
   RunnableDemo( ) {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: New");
   }

   public void run() {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Running");
      for(int i = 4; i > 0; i--) {
         try {
            Thread.sleep(49);
         } catch (InterruptedException e) {
            // TODO Auto-generated catch block
         e.printStackTrace();
         }
         System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i);
      }
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Dead");
   }
}

public class TestThread {
   public static void main(String args[]) throws InterruptedException {
      Thread t1 = new Thread( new RunnableDemo(), "Thread-1");
      Thread t2 = new Thread( new RunnableDemo(), "Thread-2");
      Thread t3 = new Thread( new RunnableDemo(), "Thread-3");

      // start t1 thread and join main thread
      t1.start();
      t1.join(200,100000);

      // t2 will start when t1 is dead or 201 ms is elapsed
      t2.start();
      t2.join(200,100000);

      // t3 will start when t2 is dead or 201 ms is elapsed
      t3.start();
   }
}
Thread: main, State: New
Thread: main, State: New
Thread: main, State: New
Thread: Thread-1, State: Running
Thread: Thread-1, 4
Thread: Thread-1, 3
Thread: Thread-1, 2
Thread: Thread-1, 1
Thread: Thread-1, State: Dead
Thread: Thread-2, State: Running
Thread: Thread-2, 4
Thread: Thread-2, 3
Thread: Thread-2, 2
Thread: Thread-2, 1
Thread: Thread-2, State: Dead
Thread: Thread-3, State: Running
Thread: Thread-3, 4
Thread: Thread-3, 3
Thread: Thread-3, 2
Thread: Thread-3, 1
Thread: Thread-3, State: Dead