Question

我有一个类ThreadClass，如下所示：

public class ThreadClass extends Thread{

    String msg;

    public void run()
    {
        for(int i=0;i<=5;i++)
        {
            System.out.println("Run method: "+msg);
        }
    }

    ThreadClass(String mg)
    {
        msg=mg;
    }

}

public class MainThreadClass {

    public static void main(String[] args) {

        ThreadClass dt1=new ThreadClass("Thread 1");
        ThreadClass dt2=new ThreadClass("Thread 2");

        dt1.start(); 
        dt2.start(); 

        System.out.println("Finished");
    }
}

我得到的输出是：

Run method: Thread 1
Finished
Run method: Thread 1
Run method: Thread 2
Run method: Thread 2
Run method: Thread 2
Run method: Thread 2
Run method: Thread 2
Run method: Thread 2
Run method: Thread 1
Run method: Thread 1
Run method: Thread 1
Run method: Thread 1

我想要实现的输出是：

Run method: Thread 1
Run method: Thread 1
Run method: Thread 2
Run method: Thread 2
Run method: Thread 2
Run method: Thread 2
Run method: Thread 2
Run method: Thread 2
Run method: Thread 1
Run method: Thread 1
Run method: Thread 1
Run method: Thread 1
Finished

因此当这两个线程终止时，打印出完成的字符串。怎么做？

Answer 1

等待每个线程使用join()退出：

public class MainThreadClass {
  public static void main(String[] args) {

    ThreadClass dt1=new ThreadClass("Thread 1");
    ThreadClass dt2=new ThreadClass("Thread 2");

    dt1.start(); 
    dt2.start(); 

    dt1.join();
    dt2.join();

    System.out.println("Finished");
  }
}

[抱歉糟糕的格式，出于某种原因，我无法让这看起来更好。可能是IE问题？]

Answer 2

您需要确定线程何时完成：

// Create and start a thread
Thread thread = new MyThread();
thread.start();

// Check if the thread has finished in a non-blocking way
if (thread.isAlive()) {
  // Thread has not finished
} else {
  // Finished
}

// Wait for the thread to finish but don't wait longer than a
// specified time
long delayMillis = 5000; // 5 seconds
try {
   thread.join(delayMillis);

  if (thread.isAlive()) {
     // Timeout occurred; thread has not finished
  } else {
     // Finished
  }
 } catch (InterruptedException e) {
    // Thread was interrupted
}

// Wait indefinitely for the thread to finish
try {
 thread.join();
  // Finished
} catch (InterruptedException e) {
  // Thread was interrupted
}

Answer 3

或者使用ExecutorService。以下是我所有类似于你的课程的摘录。

ExecutorService l_service = Executors.newFixedThreadPool(l_number_threads);
List<Future<T>> l_results = null;
try {
  l_results = l_service.invokeAll(a_tasks);
} catch (InterruptedException ex) {
  throw ex;
}
l_service.shutdownNow();

Java线程问题

3 个答案: