Java ThreadGroup 类

描述

Java ThreadGroup checkAccess()方法确定当前运行的线程是否有权修改此线程组。

声明

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

public void checkAccess()

参数

无

返回值

此方法不返回任何值。

异常

SecurityException 如果当前线程不允许访问此线程组。

示例 1

以下示例显示在单个 ThreadGroup 对象的情况下 ThreadGroup checkAccess() 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 checkAccess() 方法，我们打印 ThreadGroup 对象的访问权限。

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();
            
         // 检查 ThreadGroup 的访问权限。
         try {
        	threadGroup.checkAccess();
            System.out.println(threadGroup.getName() + " has access" );
         } catch (SecurityException ex) {
            System.out.println("No access: " + ex.toString());
         }

         // 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...
ThreadGroup has access
Thread-0 finished executing.
Thread-1 finished executing.

示例 2

以下示例显示了在多个 ThreadGroup 对象的情况下 ThreadGroup checkAccess() 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 checkAccess() 方法，我们打印两个 ThreadGroup 对象的访问权限。

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();
            
         // 检查这些线程组的访问权限。
         try {
        	pThreadGroup.checkAccess();
            System.out.println(pThreadGroup.getName() + " has access" );
        	cThreadGroup.checkAccess();
            System.out.println(cThreadGroup.getName() + " has access" );
         } catch (SecurityException ex) {
            System.out.println("No access: " + ex.toString());
         }

         // 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...
Parent ThreadGroup has access
Child ThreadGroup has access
Thread-0 finished executing.
Thread-1 finished executing.

示例 3

以下示例显示了 ThreadGroup checkAccess() 方法在子 ThreadGroup 和孙 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 checkAccess() 方法，我们打印所有 ThreadGroup 对象的访问权限。

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();
            
         // 检查这些线程组的访问权限。
         try {
        	pThreadGroup.checkAccess();
            System.out.println(pThreadGroup.getName() + " has access" );
        	cThreadGroup.checkAccess();
            System.out.println(cThreadGroup.getName() + " has access" );
			gThreadGroup.checkAccess();
            System.out.println(gThreadGroup.getName() + " has access" );
         } catch (SecurityException ex) {
            System.out.println("No access: " + ex.toString());
         }

         // 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() {
      System.out.println(Thread.currentThread().getName() + " started executing.");
      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...
Parent ThreadGroup has access
Child ThreadGroup has access
GrandChild ThreadGroup has access
Thread-0 finished executing.
Thread-1 finished executing.