Java - ThreadGroup checkAccess() Method



Description

The Java ThreadGroup checkAccess() method determines if the currently running thread has permission to modify this thread group.

Declaration

Following is the declaration for java.lang.ThreadGroup.checkAccess() method

public void checkAccess()

Parameters

NA

Return Value

This method does not return any value.

Exception

SecurityException − if the current thread is not allowed to access this thread group.

Example 1

The following example shows the usage of ThreadGroup checkAccess() method in case of a single ThreadGroup object. We've created a ThreadGroup object and assigned it a name. Then we've created two threads using the threadgroup object created earlier. Using checkAccess() method, we're printing the access rights of ThreadGroup object.

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();
            
         // checking the access for the ThreadGroup.
         try {
        	threadGroup.checkAccess();
            System.out.println(threadGroup.getName() + " has access" );
         } catch (SecurityException ex) {
            System.out.println("No access: " + ex.toString());
         }

         // 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.");
   }
} 

Output

Let us compile and run the above program, this will produce the following result −

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

Example 2

The following example shows the usage of ThreadGroup checkAccess() method in case of multiple ThreadGroup objects. We've created a ThreadGroup object and assigned it a name. As next, we've created a child ThreadGroup object. Then we've created two threads using the threadgroup objects created earlier. Using checkAccess() method, we're printing the access rights of both ThreadGroup objects.

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();
            
         // checking the access for these ThreadGroups.
         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());
         }

         // 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.");
   }
} 

Output

Let us compile and run the above program, this will produce the following result −

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

Example 3

The following example shows the usage of ThreadGroup checkAccess() method in case of child and grandchild ThreadGroup objects. We've created a ThreadGroup object and assigned it a name. As next, we've created a child ThreadGroup object. Then we've created two threads using the child and grandchild threadgroup objects created earlier. Using checkAccess() method, we're printing the access rights of all ThreadGroup objects.

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();
            
         // checking the access for these ThreadGroups.
         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());
         }

         // block until the other threads finish
         t1.join();
         t2.join();
      } catch (InterruptedException ex) {
         System.out.println(ex.toString());
      }
   }

   // implements 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 Auto-generated catch block
            e.printStackTrace();
         }  
      }
      System.out.println(Thread.currentThread().getName() + " finished executing.");
   }
} 

Output

Let us compile and run the above program, this will produce the following result −

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.
java_lang_threadgroup.htm
Advertisements