Java 线程控制

核心Java提供了对多线程程序的完全控制。您可以根据需求开发一个可以暂停、恢复或完全停止的多线程程序。有多种静态方法可以在线程对象上使用，以控制它们的行为。下表列出了这些方法：

序号	方法和描述
1	public void suspend() 此方法将线程置于挂起状态，并可以使用resume()方法恢复。
2	public void stop() 此方法完全停止线程。
3	public void resume() 此方法恢复已使用suspend()方法挂起的线程。
4	public void wait() 使当前线程等待，直到另一个线程调用notify()。
5	public void notify() 唤醒等待此对象监视器的单个线程。

请注意，最新版本的Java已经不再建议使用suspend()，resume()和stop()方法，因此你需要使用可用的替代方法。

示例

class RunnableDemo implements Runnable {
   public Thread t;
   private String threadName;
   boolean suspended = false;

   RunnableDemo( String name) {
      threadName = name;
      System.out.println("Creating " +  threadName );
   }

   public void run() {
      System.out.println("Running " +  threadName );
      try {
         for(int i = 10; i > 0; i--) {
            System.out.println("Thread: " + threadName + ", " + i);
            // Let the thread sleep for a while.
            Thread.sleep(300);
            synchronized(this) {
               while(suspended) {
                  wait();
               }
            }
         }
      } catch (InterruptedException e) {
         System.out.println("Thread " +  threadName + " interrupted.");
      }
      System.out.println("Thread " +  threadName + " exiting.");
   }

   public void start () {
      System.out.println("Starting " +  threadName );
      if (t == null) {
         t = new Thread (this, threadName);
         t.start ();
      }
   }

   void suspend() {
      suspended = true;
   }

   synchronized void resume() {
      suspended = false;
      notify();
   }
}

public class TestThread {

   public static void main(String args[]) {

      RunnableDemo R1 = new RunnableDemo( "Thread-1");
      R1.start();

      RunnableDemo R2 = new RunnableDemo( "Thread-2");
      R2.start();

      try {
         Thread.sleep(1000);
         R1.suspend();
         System.out.println("Suspending First Thread");
         Thread.sleep(1000);
         R1.resume();
         System.out.println("Resuming First Thread");

         R2.suspend();
         System.out.println("Suspending thread Two");
         Thread.sleep(1000);
         R2.resume();
         System.out.println("Resuming thread Two");
      } catch (InterruptedException e) {
         System.out.println("Main thread Interrupted");
      }try {
         System.out.println("Waiting for threads to finish.");
         R1.t.join();
         R2.t.join();
      } catch (InterruptedException e) {
         System.out.println("Main thread Interrupted");
      }
      System.out.println("Main thread exiting.");
   }
}

上述程序产生以下输出 −

输出

Creating Thread-1
Starting Thread-1
Creating Thread-2
Starting Thread-2
Running Thread-1
Thread: Thread-1, 10
Running Thread-2
Thread: Thread-2, 10
Thread: Thread-1, 9
Thread: Thread-2, 9
Thread: Thread-1, 8
Thread: Thread-2, 8
Thread: Thread-1, 7
Thread: Thread-2, 7
Suspending First Thread
Thread: Thread-2, 6
Thread: Thread-2, 5
Thread: Thread-2, 4
Resuming First Thread
Suspending thread Two
Thread: Thread-1, 6
Thread: Thread-1, 5
Thread: Thread-1, 4
Thread: Thread-1, 3
Resuming thread Two
Thread: Thread-2, 3
Waiting for threads to finish.
Thread: Thread-1, 2
Thread: Thread-2, 2
Thread: Thread-1, 1
Thread: Thread-2, 1
Thread Thread-1 exiting.
Thread Thread-2 exiting.
Main thread exiting.