Java - ThreadGroup setDaemon() 方法

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描述

Java ThreadGroup setDaemon() 方法更改此執行緒組的守護程序狀態。當其最後一個執行緒停止或其最後一個執行緒組被銷燬時，守護程序執行緒組會自動銷燬。

宣告

以下是 java.lang.ThreadGroup.setDaemon() 方法的宣告

public final void setDaemon(boolean daemon)

引數

daemon − 如果為 true，則將此執行緒組標記為守護程序執行緒組；否則，將此執行緒組標記為普通執行緒組。

返回值

此方法不返回值。

異常

SecurityException − 如果當前執行緒無法修改此執行緒組。

在 ThreadGroup 物件中設定守護程序執行緒示例

以下示例顯示了在單個 ThreadGroup 物件的情況下使用 ThreadGroup setDaemon() 方法的情況。我們建立了一個 ThreadGroup 物件併為其分配了一個名稱。然後，我們使用前面建立的 threadgroup 物件建立了兩個執行緒。使用 setDaemon() 方法，我們將其設定為守護程序執行緒組。使用 isDaemon() 方法，我們獲取此執行緒組物件的父級的狀態。

package com.tutorialspoint;

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

   public void start() {
      try {     
         // create a ThreadGroup
         ThreadGroup threadGroup = new ThreadGroup("ThreadGroup");
         // daemon status is set to true
         threadGroup.setDaemon(true);
         
         // create a thread
         Thread t1 = new Thread(threadGroup, this);
         System.out.println("Starting " + t1.getName() + "...");
         t1.start();
            
         // create another thread
         Thread t2 = new Thread(threadGroup, this);
         System.out.println("Starting " + t2.getName() + "...");
         t2.start();

         // returns true if this thread group is a daemon thread group
         System.out.println("Is " + threadGroup.getName() + " a daemon ThreadGroup? " 
            + threadGroup.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 < 4;i++) {
         i++;
         try {
			Thread.sleep(50);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
      }
      System.out.println(Thread.currentThread().getName() + " finished executing.");
   }
}

輸出

讓我們編譯並執行上述程式，這將產生以下結果：

Starting Thread-0...
Starting Thread-1...
Is ThreadGroup a daemon ThreadGroup? true
Thread-1 finished executing.
Thread-0 finished executing.

在多個 ThreadGroup 物件中設定守護程序執行緒示例

以下示例顯示了在多個 ThreadGroup 物件的情況下使用 ThreadGroup isDaemon() 方法的情況。我們建立了一個 ThreadGroup 物件併為其分配了一個名稱。接下來，我們建立了一個子 ThreadGroup 物件。使用 setDaemon() 方法，我們將其設定為守護程序執行緒組。然後，我們使用前面建立的 threadgroup 物件建立了兩個執行緒。使用 isDaemon() 方法，我們列印每個 threadgroup 物件的狀態。

package com.tutorialspoint;

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

   public void start() {
      try {     
         // create a parent ThreadGroup
         ThreadGroup pThreadGroup = new ThreadGroup("parent ThreadGroup");
		 
         // create a child ThreadGroup for parent ThreadGroup
         ThreadGroup cThreadGroup = new ThreadGroup(pThreadGroup, "child ThreadGroup");
         // daemon status is set to true
         cThreadGroup.setDaemon(true);
         // create a thread
         Thread t1 = new Thread(pThreadGroup, this);
         System.out.println("Starting " + t1.getName() + "...");
         t1.start();
            
         // create another thread
         Thread t2 = new Thread(cThreadGroup, this);
         System.out.println("Starting " + t2.getName() + "...");
         t2.start();

         // returns the status of thread group
         System.out.println("Is " + pThreadGroup.getName() 
            + " a daemon ThreadGroup? " + pThreadGroup.isDaemon());
         System.out.println("Is " + cThreadGroup.getName() 
            + " a daemon ThreadGroup? " + cThreadGroup.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 < 4;i++) {
         i++;
         try {
			Thread.sleep(50);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
      }
      System.out.println(Thread.currentThread().getName() + " finished executing.");
   }
}

輸出

讓我們編譯並執行上述程式，這將產生以下結果：

Starting Thread-0...
Starting Thread-1...
Is parent ThreadGroup a daemon ThreadGroup? false
Is child ThreadGroup a daemon ThreadGroup? true
Thread-1 finished executing.
Thread-0 finished executing.

在子/孫 ThreadGroup 物件中設定守護程序執行緒示例

以下示例顯示了在子執行緒組和孫執行緒組物件的情況下使用 ThreadGroup isDaemon() 方法的情況。我們建立了一個 ThreadGroup 物件併為其分配了一個名稱。接下來，我們建立了一個子 ThreadGroup 物件。使用 setDaemon() 方法，我們將父執行緒組設定為守護程序執行緒組。然後，我們使用前面建立的子執行緒組和孫執行緒組物件建立了兩個執行緒。使用 isDaemon() 方法，我們列印每個 threadgroup 物件的狀態。由於父執行緒組設定為守護程序，因此其子執行緒組和祖先執行緒組也成為守護程序。

package com.tutorialspoint;

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

   public void start() {
      try {     
         // create a parent ThreadGroup
         ThreadGroup pThreadGroup = new ThreadGroup("Parent ThreadGroup");
		 // daemon status is set to true
         pThreadGroup.setDaemon(true);
         // create a child ThreadGroup for parent ThreadGroup
         ThreadGroup cThreadGroup = new ThreadGroup(pThreadGroup, "Child ThreadGroup");
		 
         // create a grandchild ThreadGroup for parent ThreadGroup
         ThreadGroup gThreadGroup = new ThreadGroup(cThreadGroup, "GrandChild ThreadGroup");

         // create a thread
         Thread t1 = new Thread(cThreadGroup, this);
         System.out.println("Starting " + t1.getName() + "...");
         t1.start();
            
         // create another thread
         Thread t2 = new Thread(gThreadGroup, this);
         System.out.println("Starting " + t2.getName() + "...");
         t2.start();
            
         // returns the status of thread group
         System.out.println("Is " + pThreadGroup.getName() 
            + " a daemon ThreadGroup? " + pThreadGroup.isDaemon());
         System.out.println("Is " + cThreadGroup.getName() 
            + " a daemon ThreadGroup? " + cThreadGroup.isDaemon());
         System.out.println("Is " + gThreadGroup.getName() 
            + " a daemon ThreadGroup? " + gThreadGroup.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 < 4;i++) {
         i++;
         try {
			Thread.sleep(50);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
      }
      System.out.println(Thread.currentThread().getName() + " finished executing.");
   }
}

輸出

讓我們編譯並執行上述程式，這將產生以下結果：

Starting Thread-0...
Starting Thread-1...
Is Parent ThreadGroup a daemon ThreadGroup? true
Is Child ThreadGroup a daemon ThreadGroup? true
Is GrandChild ThreadGroup a daemon ThreadGroup? true
Thread-0 finished executing.
Thread-1 finished executing.
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