Java.lang.ThreadGroup.isDaemon() 方法

描述

java.lang.ThreadGroup.isDaemon() 方法测试这个线程组是否是一个守护线程组。 守护线程组在其最后一个线程停止或其最后一个线程组被销毁时自动销毁。

声明

以下是 java.lang.ThreadGroup.isDaemon() 方法的声明。

public final boolean isDaemon()

参数

NA

返回值

如果此线程组是守护线程组，则此方法返回 true，否则返回 false。

异常

NA

示例

下面的例子展示了 java.lang.ThreadGroup.isDaemon() 方法的使用。

package com.tutorialspoint;

import java.lang.*;

public class ThreadGroupDemo implements Runnable {
   public static void main(String[] args) {
      ThreadGroupDemo tg = new ThreadGroupDemo();
      tg.func();
   }

   public void func() {
      try {     
         // create a parent ThreadGroup
         ThreadGroup pGroup = new ThreadGroup("Parent ThreadGroup");
    
         // create a child ThreadGroup for parent ThreadGroup
         ThreadGroup cGroup = new ThreadGroup(pGroup, "Child ThreadGroup");

         // create a thread
         Thread t1 = new Thread(pGroup, this);
         System.out.println("Starting " + t1.getName() + "...");
         t1.start();
            
         // create another thread
         Thread t2 = new Thread(cGroup, this);
         System.out.println("Starting " + t2.getName() + "...");
         t2.start();
            
         // display the number of active threads 
         System.out.println("Active threads in " + pGroup.getName() 
            + " = " + pGroup.activeCount());

         // returns true if this thread group is a daemon thread group
         System.out.println("Is " + pGroup.getName() + " a daemon
            ThreadGroup? " + pGroup.isDaemon());
         System.out.println("Is " + cGroup.getName() + " a daemon
            ThreadGroup? " + cGroup.isDaemon());

         // block until the other threads finish
         t1.join();
         t2.join();
      } catch (InterruptedException ex) {
         System.out.println(ex.toString());
      }
   }

   // implements run()
   public void run() {

      for(int i = 0;i < 1000;i++) {
         i++;
      }
      System.out.println(Thread.currentThread().getName() + " finished executing.");
   }
} 

让我们编译并运行上面的程序，这将产生下面的结果 −

Starting Thread-0...
Starting Thread-1...
Active threads in Parent ThreadGroup = 2
Is Parent ThreadGroup a daemon ThreadGroup? false
Is Child ThreadGroup a daemon ThreadGroup? false
Thread-0 finished executing.
Thread-1 finished executing.