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Java - 线程连接

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创建 Thread 对象后，可以通过调用 start() 方法来启动它，该方法会执行对 run() 方法的调用。在多个线程运行的情况下，我们可以阻塞当前线程，直到另一个线程终止。

Java 中的线程连接

Java 中的线程连接是指等待（或阻塞）一个线程，直到另一个线程完成其执行。 Thread 类的 join() 方法用于此目的。

语法

以下是 join() 方法的简单语法：

void join();

重载的 Thread.join() 方法

以下是三个重载的 join() 方法：

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。
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指定的毫秒数过去。
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指定的毫秒数 + 纳秒数过去。

Java 中线程连接的示例

在此示例中，我们通过实现 Runnable 接口创建一个 RunnableDemo 类。RunnableDemo 类具有 run() 方法的实现。在主类 TestThread 中，我们创建了 RunnableDemo 对象，并使用这些对象创建了两个 Thread 对象。当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，我们阻塞当前线程，以确保一旦一个线程完成，只有下一个线程才会启动。

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();
   }
}

输出

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

Java 中线程连接的更多示例

示例 1

在此示例中，我们通过实现 Runnable 接口创建一个 RunnableDemo 类。RunnableDemo 类具有 run() 方法的实现。在主类 TestThread 中，我们创建了 RunnableDemo 对象，并使用这些对象创建了两个 Thread 对象。当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，我们将当前线程阻塞 200 毫秒，以确保一旦一个线程完成或延迟 200 毫秒后，只有下一个线程才会启动。

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();
   }
}

输出

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

示例 2

在此示例中，我们通过实现 Runnable 接口创建一个 RunnableDemo 类。RunnableDemo 类具有 run() 方法的实现。在主类 TestThread 中，我们创建了 RunnableDemo 对象，并使用这些对象创建了两个 Thread 对象。当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，我们将当前线程阻塞 200 毫秒和 100000 纳秒，以确保一旦一个线程完成或延迟 201 毫秒后，只有下一个线程才会启动。

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();
   }
}

输出

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

打印页面

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