Java ThreadPoolExecutor getActiveCount() Method

The getActiveCount() method of ThreadPoolExecutor class returns the approximate number of threads that are actively executing the tasks.

Syntax

Parameters

Returns

The number of threads

Throw

Does not throw the exception.

Example 1

import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.lang.Thread;
public class ThreadPoolExecutorgetActiveCountExample1  {	
   public static void main(final String[] arguments) throws InterruptedException {
        ThreadPoolExecutor executor = (ThreadPoolExecutor)Executors.newCachedThreadPool();
        System.out.println("Currently executing threads: "+ executor.getActiveCount());
        executor.submit(new Task());
        executor.submit(new Task());
        executor.shutdown();
      }  
      static class Task implements Runnable {
      @Override
      public void run() {
          try {
              Long duration = (long) (Math.random() * 5);
              System.out.println("Running Thread Name: " + Thread.currentThread().getName());
              TimeUnit.SECONDS.sleep(duration);
              System.out.println("Completed Thread Name: " +Thread.currentThread().getName());
            } catch (InterruptedException e) {
          }
        }
     }
}

Test it Now

Output:

Currently executing threads: 0
Running Thread Name: pool-1-thread-2
Running Thread Name: pool-1-thread-1
Completed Thread Name: pool-1-thread-1
Completed Thread Name: pool-1-thread-2

Example 2

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.lang.Thread;
import java.util.logging.Level;
import java.util.logging.Logger;
public class ThreadPoolExecutorgetActiveCountExample2   {
  public static void main(String[] args) {
    Task4 task1 = new Task4("t1");
      System.out.println("Starting threads");
    ThreadPoolExecutor tExecutor = (ThreadPoolExecutor) Executors.newCachedThreadPool();
     System.out.println(" Before execute Currently executing threads: "+ tExecutor.getActiveCount());
    tExecutor.execute(task1); // start task1
    System.out.println(" After execute Currently executing threads: "+ tExecutor.getActiveCount());
    tExecutor.shutdown(); // shutdown worker threads
    System.out.println("Threads started, main ends\n");
  }
}
class Task4 implements Runnable {
  private final String threadName;
  public Task4(String threadName) {
    this.threadName = threadName;
   }
  
  @Override
  public void run() {
      for(int i=0 ; i<=10;i++)
      {
          if(i<5)
          {
              try {
                  System.out.println("Thread sleeping for 1000 i=" +i);
                  Thread.sleep(1000);
                  } catch (InterruptedException ex) {
                  Logger.getLogger(Task4.class.getName()).log(Level.SEVERE, null, ex);
              }
          }
          else{
              System.out.println(" now  i > 5 :");
              break;
          }
      }
}
}

Test it Now

Output:

Starting threads
 Before execute Currently executing threads: 0
 After execute Currently executing threads: 1
Thread sleeping for 1000 i=0
Threads started, main ends

Thread sleeping for 1000 i=1
Thread sleeping for 1000 i=2
Thread sleeping for 1000 i=3
Thread sleeping for 1000 i=4
 now  i > 5 :

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