Java Executors newCachedThreadPool() Method

The newCachedThreadPool() method of Executors class creates a thread pool that creates new threads as needed but will reuse previously constructed threads when they are available.

Syntax

public static ExecutorService newCachedThreadPool()
public static ExecutorService newCachedThreadPool (ThreadFactory threadFactory)

Parameter

threadFactory - the factory to use when creating new threads

Returns

the newly created thread pool

Throws

NullPointerException

Example 1

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class ExecutornewCachedThreadPoolExample1  {
	
   public static void main(final String[] arguments) throws InterruptedException {
      ExecutorService excr = Executors.newCachedThreadPool();
      ThreadPoolExecutor mypool = (ThreadPoolExecutor) excr;
//print statement will print the pool size.
      System.out.println("size of mypool: " + mypool.getPoolSize());
      excr.submit(new Threadimpl());
      excr.submit(new Threadimpl());
      System.out.println("Total number threads scheduled): "+ mypool.getTaskCount());
      excr.shutdown();
   }  

   static class Threadimpl implements Runnable {

      public void run() {
         
         try {
            Long num = (long) (Math.random() / 30);
            System.out.println("Thread Name: " +Thread.currentThread().getName());
               TimeUnit.SECONDS.sleep(num);
            System.out.println("after sleep Thread Name: " +Thread.currentThread().getName());
         } catch (InterruptedException e) {
            e.printStackTrace();
         }
      }
   }
}

Test it Now

Output:

size of mypool: 0
Total number threads scheduled): 2
Thread Name: pool-1-thread-2
Thread Name: pool-1-thread-1
after sleep Thread Name: pool-1-thread-2
after sleep Thread Name: pool-1-thread-1

Example 2

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class ExecutornewCachedThreadPoolExample2  {
	
   public static void main(final String[] arguments) throws InterruptedException {
       ThreadFactory ThreadFactory = Executors.defaultThreadFactory();
      ExecutorService excr = Executors.newCachedThreadPool(ThreadFactory);
      ThreadPoolExecutor mypool = (ThreadPoolExecutor) excr;
      System.out.println("size of mypool: " + mypool.getPoolSize());
      for(int i=0 ; i<= 4 ; i++) {
      excr.submit(new Threadimpl());
      }
      excr.shutdown();
   }  

   static class Threadimpl implements Runnable {

      public void run() {
         
         try {
            Long num = (long) (Math.random() / 30);
            System.out.println("Thread Name: " +Thread.currentThread().getName());
               TimeUnit.SECONDS.sleep(num);
            System.out.println("after sleep Thread Name: " +Thread.currentThread().getName());
         } catch (InterruptedException e) {
            e.printStackTrace();
         }
      }
   }
}

Test it Now

Output:

Thread Name: pool-1-thread-4
after sleep Thread Name: pool-1-thread-4
Thread Name: pool-1-thread-3
after sleep Thread Name: pool-1-thread-3
Thread Name: pool-1-thread-1
after sleep Thread Name: pool-1-thread-1

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