newFixedThreadPool Method

A fixed thread pool can be obtainted by calling the static newFixedThreadPool() method of Executors class.

Syntax

ExecutorService fixedPool = Executors.newFixedThreadPool(2);

where

• Maximum 2 threads will be active to process tasks.
• If more than 2 threads are submitted then they are held in a queue until threads become available.
• A new thread is created to take its place if a thread terminates due to failure during execution shutdown on executor is not yet called.
• Any thread exists till the pool is shutdown.

Example

The following TestThread program shows usage of newFixedThreadPool method in thread based environment.

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

public class TestThread {
	
   public static void main(final String[] arguments) throws InterruptedException {
  ExecutorService executor = Executors.newFixedThreadPool(2);
  // Cast the object to its class type
  ThreadPoolExecutor pool = (ThreadPoolExecutor) executor;
  //Stats before tasks execution
  System.out.println("Largest executions: "
     + pool.getLargestPoolSize());
  System.out.println("Maximum allowed threads: "
     + pool.getMaximumPoolSize());
  System.out.println("Current threads in pool: "
     + pool.getPoolSize());
  System.out.println("Currently executing threads: "
     + pool.getActiveCount());
  System.out.println("Total number of threads(ever scheduled): "
     + pool.getTaskCount());
  executor.submit(new Task());
  executor.submit(new Task());
  //Stats after tasks execution
  System.out.println("Core threads: " + pool.getCorePoolSize());
  System.out.println("Largest executions: "
     + pool.getLargestPoolSize());
  System.out.println("Maximum allowed threads: "
     + pool.getMaximumPoolSize());
  System.out.println("Current threads in pool: "
     + pool.getPoolSize());
  System.out.println("Currently executing threads: "
     + pool.getActiveCount());
  System.out.println("Total number of threads(ever scheduled): "
     + pool.getTaskCount());
  executor.shutdown();
   }  

   static class Task implements Runnable {

  public void run() {
     
     try {
        Long duration = (long) (Math.random() * 5);
        System.out.println("Running Task! Thread Name: " +
           Thread.currentThread().getName());
           TimeUnit.SECONDS.sleep(duration);
        
        System.out.println("Task Completed! Thread Name: " +
           Thread.currentThread().getName());
     } catch (InterruptedException e) {
        e.printStackTrace();
     }
  }
   }
}

This will produce the following result.

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Output

Largest executions: 0
Maximum allowed threads: 2
Current threads in pool: 0
Currently executing threads: 0
Total number of threads(ever scheduled): 0
Core threads: 2
Largest executions: 2
Maximum allowed threads: 2
Current threads in pool: 2
Currently executing threads: 1
Total number of threads(ever scheduled): 2
Running Task! Thread Name: pool-1-thread-1
Running Task! Thread Name: pool-1-thread-2
Task Completed! Thread Name: pool-1-thread-2
Task Completed! Thread Name: pool-1-thread-1