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Java - ThreadGroup activeCount() Method
Description
The Java ThreadGroup activeCount() method returns an estimate of the number of active threads in this thread group.
Declaration
Following is the declaration for java.lang.ThreadGroup.activeCount() method
public int activeCount()
Parameters
NA
Return Value
This method returns an estimate of the number of active threads in this thread group and in any other thread group that has this thread group as an ancestor.
Exception
NA
Example 1
The following example shows the usage of ThreadGroup activeCount() 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 activeCount() method, we're printing the active thread count.
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 threads in \"" + threadGroup.getName() + "\" = " + threadGroup.activeCount()); // 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... Active threads in "ThreadGroup" = 2 Thread-0 finished executing. Thread-1 finished executing.
Example 2
The following example shows the usage of ThreadGroup activeCount() 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 activeCount() method, we're printing the active thread count in parent ThreadGroup object as well as child 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 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 threads in \"" + pThreadGroup.getName() + "\" = " + pThreadGroup.activeCount()); System.out.println("Active threads in \"" + cThreadGroup.getName() + "\" = " + cThreadGroup.activeCount()); // 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... Active threads in "Parent ThreadGroup" = 2 Active threads in "Child ThreadGroup" = 1 Thread-0 finished executing. Thread-1 finished executing.
Example 3
The following example shows the usage of ThreadGroup activeCount() method in case of child ThreadGroup object. 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 threadgroup object created earlier. Using activeCount() method, we're printing the active thread count in parent ThreadGroup object as well as child 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 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(cThreadGroup, 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 threads in \"" + pThreadGroup.getName() + "\" = " + pThreadGroup.activeCount()); System.out.println("Active threads in \"" + cThreadGroup.getName() + "\" = " + cThreadGroup.activeCount()); // 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... Active threads in "Parent ThreadGroup" = 2 Active threads in "Child ThreadGroup" = 2 Thread-1 finished executing. Thread-0 finished executing.
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