java.lang.ThreadGroup.isDaemon() 方法测试此线程组是否为一个后台程序线程组。当其最后一个线程被停止或它的最后一个线程组被销毁守护线程组会自动销毁。

声明

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

public final boolean isDaemon()

参数

• NA

返回值

如果此线程组是一个后台程序线程组此方法返回true，否则返回false。

异常

• NA

例子

下面的例子显示java.lang.ThreadGroup.isDaemon()方法的使用。

package com.yiibai;

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.");
   }
} 

让我们来编译和运行上面的程序，这将产生以下结果：

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.