java.lang.ThreadGroup.isDaemon() 方法測試此線程組是否為一個後台程序線程組。當其最後一個線程被停止或它的最後一個線程組被銷毀守護線程組會自動銷毀。

聲明

以下是java.lang.ThreadGroup.isDaemon()方法的聲明

public final boolean isDaemon()

參數

• NA

返回值

如果此線程組是一個後台程序線程組此方法返回true，否則返回false。

異常

• NA

例子

下麵的例子顯示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.");
   }
} 

讓我們來編譯和運行上麵的程序，這將產生以下結果：

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.