Java ThreadPoolExecutor setCorePoolSize() Method

The setCorePoolSize() method of ThreadPoolExecutor class sets the core number of threads in the pool. This method accepts the size of the pool as a parameter.

Syntax

Parameters

corePoolSize - the new core size

Return

Throw

IllegalArgumentException - if corePoolSize < 0 or corePoolSize is greater than the maximum pool size

Example 1

import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.lang.Thread;
public class ThreadPoolExecutorsetCorePoolsizeExample1  {
public static void main(final String[] arguments) throws InterruptedException {
             ThreadPoolExecutor executor = (ThreadPoolExecutor)Executors.newCachedThreadPool();
             executor.submit(new Task());
             executor.submit(new Task());
             executor.setCorePoolSize(5);
             System.out.println("Core Pool size after execution: " + executor.getCorePoolSize());
             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:

Core Pool size after execution: 5
Running Thread Name: pool-1-thread-1
Running Thread Name: pool-1-thread-2
Completed Thread Name: pool-1-thread-2
Completed Thread Name: pool-1-thread-1

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 ThreadPoolExecutorsetCorePoolsizeExample2    {
                   public static void main(String[] args) {
                                  Task8 task1 = new Task8("t1");
                                  Task8 task2 = new Task8("t2");
                                  System.out.println("Starting threads");
                          ThreadPoolExecutor tExecutor = (ThreadPoolExecutor) Executors.newCachedThreadPool();
                          tExecutor.execute(task1); tExecutor.execute(task2); // start task1
                          tExecutor.setCorePoolSize(5);
                          System.out.println(" After execute Core pool size : "+ tExecutor.getCorePoolSize());
                          tExecutor.shutdown(); // shutdown worker threads
                          System.out.println("Threads started, main ends\n");
                            }
                   }
class Task8 implements Runnable {
             private final String threadName;
             public Task8(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(Task8.class.getName()).log(Level.SEVERE, null, ex);
                       }
                   }
                  else{
                       System.out.println(" now  i > 5 :");
                       break;
                    }
               }
                   }
}

Test it Now

Output:

Starting threads
 After execute Core pool size : 5
Thread sleeping for 1000 i=0
Thread sleeping for 1000 i=0
Threads started, main ends

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

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