Question

我是Java的初学者。我想通过生成一个Thread来实现一个Timer。我想要运行的方式是主线程即使在产生线程后也应该继续工作。但是一旦线程完成Task，它应该通知主线程任务完成。我查看了Thread.join（）和Thread.sleep（）。对于这两种方法，主线程等待线程完成任务。但是我希望主线程继续运行。

我在下面编写了一个代码，主线程调用一个线程，线程执行任务10秒。但是我无法通知主线程有关任务完成的信息。请帮助我。

public class MainThreadtest {
   public static void main(String[] args) {
      dispthread2 dt2 = new dispthread2();
      dt2.start();
      System.out.println("Thread dt2 has started");
   }
}

第二课

public class dispthread2 extends Thread {
   public void run() {
      long endTimemillis = System.currentTimeMillis() + 10000;
      while (System.currentTimeMillis() < endTimemillis) {
      }
      System.out.println("The task is done");
   }
}

Answer 1

解决此问题的一种方法是不需要使用Thread＃join，从而允许两个线程独立运行：

使用Observer Pattern侦听器接口，例如可以通过Java Beans PropertyChangeSupport和PropertyChangeListener获取。
不要扩展Thread，而是实现Runnable。

例如：

import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;

import javax.swing.event.SwingPropertyChangeSupport;

public class MainThreadTest {
   public static void main(String[] args) {
      DispThread2 dt2 = new DispThread2();
      dt2.addPropertyChangeListener(DispThread2.STATE, new PropertyChangeListener() {

         @Override
         public void propertyChange(PropertyChangeEvent evt) {
            System.out.println("DT2 Thread state (from Main Thread): " + evt.getNewValue());
            if (evt.getNewValue() == DispThreadState.DONE) {
               System.out.println("Thread dt2 is now done (from Main Thread)");
            }
         }
      });
      new Thread(dt2, "DT2").start();
      System.out.println("Thread dt2 has started");
   }
}

class DispThread2 implements Runnable {
   public static final String STATE = "state";
   private volatile DispThreadState state = DispThreadState.PENDING;
   private PropertyChangeSupport support = new SwingPropertyChangeSupport(this);

   public void addPropertyChangeListener(PropertyChangeListener listener) {
      support.addPropertyChangeListener(listener);
   }

   public void addPropertyChangeListener(String propertyName, PropertyChangeListener listener) {
      support.addPropertyChangeListener(propertyName, listener);
   }

   public void removePropertyChangeListener(PropertyChangeListener listener) {
      support.removePropertyChangeListener(listener);
   }

   public void run() {
      setState(DispThreadState.RUNNING);
      long endTimemillis = System.currentTimeMillis() + 10000;
      while (System.currentTimeMillis() < endTimemillis) {
      }
      System.out.println("The task is done");
      setState(DispThreadState.DONE);
   }

   public DispThreadState getState() {
      return state;
   }

   public void setState(DispThreadState state) {
      DispThreadState oldValue = this.state;
      DispThreadState newValue = state;
      this.state = state;
      support.firePropertyChange(STATE, oldValue, newValue);
   }
}

enum DispThreadState {
   PENDING, RUNNING, DONE
}

当主线程仍在运行时，Thread如何通知主线程

1 个答案: