Java ThreadPoolExecutor setMaximumPoolSize() Method

The setMaximumPoolSize () method of the ThreadPoolExecutor class sets the maximum number of threads allowed. This overrides any value set in the constructor.

Syntax

Parameters

maximumPoolSize - the new maximum

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 ThreadPoolExecutorsetMaximumPoolSizeExample1   {
  public static void main(final String[] arguments) throws InterruptedException {
        ThreadPoolExecutor executor = (ThreadPoolExecutor)Executors.newCachedThreadPool();
        executor.setMaximumPoolSize(10);
        System.out.println("MAXIMUM POOL SIZE BEFORE SUBMIT: "+ executor.getMaximumPoolSize());
        executor.submit(new Task());
        executor.submit(new Task());
        executor.shutdown();
        System.out.println(" POOL SIZE AFTER SUBMIT:"+ executor.getLargestPoolSize());
      }  
     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:

MAXIMUM POOL SIZE BEFORE SUBMIT: 10
 POOL SIZE AFTER SUBMIT:2
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 ThreadPoolExecutorsetMaximumPoolSizeExample2     {
  public static void main(String[] args) {
    Tsk task1 = new Tsk("t1");
    Tsk task2 = new Tsk("t2");
    System.out.println("Starting threads");
    ThreadPoolExecutor tExecutor = (ThreadPoolExecutor) Executors.newCachedThreadPool();
    tExecutor.setMaximumPoolSize(7);
     System.out.println("  Maximum pool size: "+ tExecutor.getMaximumPoolSize());
     tExecutor.submit(task1); tExecutor.submit(task2); 
    tExecutor.execute(task1); // start task1
    tExecutor.execute(task2); // start task2    
    System.out.println(" After submit largest pool size: "+ tExecutor.getLargestPoolSize());
    tExecutor.shutdown(); // shutdown worker threads
    System.out.println("Threads started, main ends\n");
  }
}
class Tsk implements Runnable {
  private final String threadName;
 public Tsk(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(Tsk.class.getName()).log(Level.SEVERE, null, ex);
              }
          }
          else{
              System.out.println(" now  i > 5 :");
              break;
          }
      }
}
}

Test it Now

Output:

Starting threads
  Maximum pool size: 7
Thread sleeping for 1000 i=0
Thread sleeping for 1000 i=0
Thread sleeping for 1000 i=0
Thread sleeping for 1000 i=0
 After submit largest pool size: 4
Threads started, main ends
Thread sleeping for 1000 i=1
Thread sleeping for 1000 i=1
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=2
Thread sleeping for 1000 i=2
Thread sleeping for 1000 i=3
Thread sleeping for 1000 i=3
Thread sleeping for 1000 i=3
Thread sleeping for 1000 i=3
Thread sleeping for 1000 i=4
Thread sleeping for 1000 i=4
Thread sleeping for 1000 i=4
Thread sleeping for 1000 i=4
 now  i > 5 :
 now  i > 5 :
 now  i > 5 :
 now  i > 5 :

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