Java - ThreadGroup activeGroupCount() 方法

描述

Java ThreadGroup activeGroupCount() 方法返回此线程组中活动组数量的估计值。

声明

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

public int activeGroupCount()

参数

无

返回值

此方法返回以此线程组为祖先的活动线程组的数量。

异常

无

在 ThreadGroup 对象中获取活动组计数示例

以下示例展示了在单个 ThreadGroup 对象的情况下 ThreadGroup activeGroupCount() 方法的用法。我们创建了一个 ThreadGroup 对象并为其指定了一个名称。然后，我们使用前面创建的 threadgroup 对象创建了两个线程。使用 activeGroupCount() 方法，我们打印活动组计数。

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");

         // 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();
            
         // display the number of active threads 
         System.out.println("Active groups in \"" + threadGroup.getName() 
            + "\" = " + threadGroup.activeGroupCount());

         // 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.");
   }
} 

让我们编译并运行上述程序，这将产生以下结果：

Starting Thread-0...
Starting Thread-1...
Active groups in "ThreadGroup" = 0
Thread-1 finished executing.
Thread-0 finished executing.

在多个 ThreadGroup 对象中获取活动组计数示例

以下示例展示了在多个 ThreadGroup 对象的情况下 ThreadGroup activeGroupCount() 方法的用法。我们创建了一个 ThreadGroup 对象并为其指定了一个名称。接下来，我们创建了一个子 ThreadGroup 对象。然后，我们使用前面创建的 threadgroup 对象创建了两个线程。使用 activeGroupCount() 方法，我们打印父 ThreadGroup 对象和子 ThreadGroup 对象中的活动组计数。

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");

         // 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();
            
         // display the number of active threads 
         System.out.println("Active groups in \"" + pThreadGroup.getName() 
            + "\" = " + pThreadGroup.activeGroupCount());
			
         System.out.println("Active groups in \"" + cThreadGroup.getName() 
            + "\" = " + cThreadGroup.activeGroupCount());

         // 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.");
   }
} 

让我们编译并运行上述程序，这将产生以下结果：

Starting Thread-0...
Starting Thread-1...
Active groups in "Parent ThreadGroup" = 1
Active groups in "Child ThreadGroup" = 0
Thread-1 finished executing.
Thread-0 finished executing.

在子/孙 ThreadGroup 对象中获取活动组计数示例

以下示例展示了在子 ThreadGroup 对象和孙 ThreadGroup 对象的情况下 ThreadGroup activeGroupCount() 方法的用法。我们创建了一个 ThreadGroup 对象并为其指定了一个名称。接下来，我们创建了一个子 ThreadGroup 对象。然后，我们使用前面创建的子 ThreadGroup 对象和孙 ThreadGroup 对象创建了两个线程。使用 activeGroupCount() 方法，我们打印所有 ThreadGroup 对象中的活动组计数。

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");
		 
         // 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();
            
         // display the number of active threads 
         System.out.println("Active groups in \"" + pThreadGroup.getName() 
            + "\" = " + pThreadGroup.activeGroupCount());
			
         System.out.println("Active groups in \"" + cThreadGroup.getName() 
            + "\" = " + cThreadGroup.activeGroupCount());
			
         System.out.println("Active groups in \"" + gThreadGroup.getName() 
            + "\" = " + gThreadGroup.activeGroupCount());

         // 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.");
   }
} 

让我们编译并运行上述程序，这将产生以下结果：

Starting Thread-0...
Starting Thread-1...
Active groups in "Parent ThreadGroup" = 2
Active groups in "Child ThreadGroup" = 1
Active groups in "GrandChild ThreadGroup" = 0
Thread-0 finished executing.
Thread-1 finished executing.