Java.lang.ThreadGroup.setDaemon() 方法

描述

java.lang.ThreadGroup.setDaemon() 方法改变了这个线程组的守护进程状态。 守护线程组在其最后一个线程停止或最后一个线程组被销毁时自动销毁。

声明

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

public final void setDaemon(boolean daemon)

参数

daemon − 如果为真，则将此线程组标记为守护线程组； 否则，将此线程组标记为正常。

返回值

此方法不返回任何值。

异常

SecurityException − 如果当前线程不能修改这个线程组。

示例

下面的例子展示了 java.lang.ThreadGroup.setDaemon() 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");
         // 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...
Is Parent ThreadGroup a daemonThreadGroup? true
Is Child ThreadGroup a daemonThreadGroup? true
Thread-0 finished executing.
Thread-1 finished executing.