java.lang.ThreadGroup.setDaemon() 方法改变该线程组的守护进程的状态。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.setDaemon()方法的声明

public final void setDaemon(boolean daemon)

参数

• daemon -- 如果为true，这标志着该线程组作为守护线程组;否则，标志着该线程组为正常。

返回值

此方法不返回任何值。

异常

• SecurityException -- 如果当前线程无法修改此线程组。

例子

下面的例子显示java.lang.ThreadGroup.setDaemon()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");
         // daemon status is set to true
         pGroup.setDaemon(true);
    
         // create a child ThreadGroup for parent ThreadGroup
         ThreadGroup cGroup = new ThreadGroup(pGroup, "Child ThreadGroup");
         // daemon status is set to true
         cGroup.setDaemon(true);

         // 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();

         // 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...
Is Parent ThreadGroup a daemonThreadGroup? true
Is Child ThreadGroup a daemonThreadGroup? true
Thread-0 finished executing.
Thread-1 finished executing.