Java ThreadGroup 类

说明

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

示例1

以下示例显示了在单个 ThreadGroup 对象的情况下 ThreadGroup activeGroupCount() 方法的用法。我们创建了一个 ThreadGroup 对象并为其分配了一个名称。然后我们使用之前创建的线程组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.yxjc123;
public class ThreadGroupDemo implements Runnable {
   public static void main(String[] args) {
      ThreadGroupDemo tg = new ThreadGroupDemo();
      tg.start();
   }
   public void start() {
      try {     
         //创建一个ThreadGroup
         ThreadGroup threadGroup = new ThreadGroup("ThreadGroup");

         //创建一个线程
         Thread t1 = new Thread(threadGroup, this);
         System.out.println("Starting " + t1.getName() + "...");
         t1.start();
            
         //创建另一个线程
         Thread t2 = new Thread(threadGroup, this);
         System.out.println("Starting " + t2.getName() + "...");
         t2.start();
            
         //显示活动线程数
         System.out.println("Active groups in \"" + threadGroup.getName() 
            + "\" = " + threadGroup.activeGroupCount());

         // 阻塞直到其他线程完成
         t1.join();
         t2.join();
      } catch (InterruptedException ex) {
         System.out.println(ex.toString());
      }
   }

   // 实现 run()
   public void run() {

      for(int i = 0; i < 4;i++) {
         i++;
         try {
            Thread.sleep(50);
         } catch (InterruptedException e) {
            // TODO 自动生成的 catch 块
            e.printStackTrace();
         }
      }
      System.out.println(Thread.currentThread().getName() + " finished executing.");
   }
}

输出

让我们编译并运行上面的程序，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.

示例 2

以下示例显示了在多个 ThreadGroup 对象的情况下 ThreadGroup activeGroupCount() 方法的用法。我们创建了一个 ThreadGroup 对象并为其分配了一个名称。接下来，我们创建了一个子 ThreadGroup 对象。然后我们使用之前创建的线程组对象创建了两个线程。使用 activeGroupCount() 方法，我们打印父 ThreadGroup 对象以及子 ThreadGroup 对象中的活动组计数。

package com.yxjc123;
public class ThreadGroupDemo implements Runnable {
   public static void main(String[] args) {
      ThreadGroupDemo tg = new ThreadGroupDemo();
      tg.start();
   }
   public void start() {
      try {     
         //创建父ThreadGroup
         ThreadGroup pThreadGroup = new ThreadGroup("Parent ThreadGroup");
		 
         //为父ThreadGroup创建子ThreadGroup
         ThreadGroup cThreadGroup = new ThreadGroup(pThreadGroup, "Child ThreadGroup");

         //创建一个线程
         Thread t1 = new Thread(pThreadGroup, this);
         System.out.println("Starting " + t1.getName() + "...");
         t1.start();
            
         //创建另一个线程
         Thread t2 = new Thread(cThreadGroup, this);
         System.out.println("Starting " + t2.getName() + "...");
         t2.start();
            
         //显示活动线程数
         System.out.println("Active groups in \"" + pThreadGroup.getName() 
            + "\" = " + pThreadGroup.activeGroupCount());
			
         System.out.println("Active groups in \"" + cThreadGroup.getName() 
            + "\" = " + cThreadGroup.activeGroupCount());

         // 阻塞直到其他线程完成
         t1.join();
         t2.join();
      } catch (InterruptedException ex) {
         System.out.println(ex.toString());
      }
   }

   // 实现 run()
   public void run() {
      for(int i = 0; i < 4;i++) {
         i++;
         try {
            Thread.sleep(50);
         } catch (InterruptedException e) {
            // TODO 自动生成的 catch 块
            e.printStackTrace();
         }
      }
      System.out.println(Thread.currentThread().getName() + " finished executing.");
   }
}

输出

让我们编译并运行上面的程序，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.

示例 3

以下示例显示了 ThreadGroup activeGroupCount() 方法在子级和孙级 ThreadGroup 对象的情况下的用法。我们创建了一个 ThreadGroup 对象并为其分配了一个名称。接下来，我们创建了一个子 ThreadGroup 对象。然后，我们使用之前创建的子线程组对象和孙线程组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.yxjc123;
public class ThreadGroupDemo implements Runnable {
   public static void main(String[] args) {
      ThreadGroupDemo tg = new ThreadGroupDemo();
      tg.start();
   }
   public void start() {
      try {     
         //创建父ThreadGroup
         ThreadGroup pThreadGroup = new ThreadGroup("Parent ThreadGroup");
		 
         //为父ThreadGroup创建子ThreadGroup
         ThreadGroup cThreadGroup = new ThreadGroup(pThreadGroup, "Child ThreadGroup");
		 
         //为父ThreadGroup创建孙ThreadGroup
         ThreadGroup gThreadGroup = new ThreadGroup(cThreadGroup, "GrandChild ThreadGroup");

         //创建一个线程
         Thread t1 = new Thread(cThreadGroup, this);
         System.out.println("Starting " + t1.getName() + "...");
         t1.start();
            
         //创建另一个线程
         Thread t2 = new Thread(gThreadGroup, this);
         System.out.println("Starting " + t2.getName() + "...");
         t2.start();
            
         //显示活动线程数
         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());

         // 阻塞直到其他线程完成
         t1.join();
         t2.join();
      } catch (InterruptedException ex) {
         System.out.println(ex.toString());
      }
   }

   // 实现 run()
   public void run() {
      for(int i = 0; i < 4;i++) {
         i++;
         try {
            Thread.sleep(50);
         } catch (InterruptedException e) {
            // TODO 自动生成的 catch 块
            e.printStackTrace();
         }
      }
      System.out.println(Thread.currentThread().getName() + " finished executing.");
   }
}

输出

让我们编译并运行上面的程序，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.