Java Executor Framework Example

import java.util.concurrent.atomic.AtomicInteger;

public class Counter {
  private AtomicInteger value = new AtomicInteger(); 
  public int getValue(){
    return value.get();
  }
  public int increment(){
    return value.incrementAndGet();
  }
  
  // Alternative implementation as increment but just make the 
  // implementation explicit
  public int incrementLongVersion(){
    int oldValue = value.get();
    while (!value.compareAndSet(oldValue, oldValue+1)){
       oldValue = value.get();
    }
    return oldValue+1;
  }
  
} 

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class Test {
    private static final int NTHREDS = 10;

    public static void main(String[] args) {
      final Counter counter = new Counter();
      List<Future<Integer>> list = new ArrayList<Future<Integer>>();

      ExecutorService executor = Executors.newFixedThreadPool(NTHREDS);
      for (int i = 0; i < 500; i++) {
        Callable<Integer> worker = new  Callable<Integer>() {
          @Override
          public Integer call() throws Exception {
            int number = counter.increment();
            System.out.println(number);
            return number ;
          }
        };
        Future<Integer> submit= executor.submit(worker);
        list.add(submit);

      }
      
      
      // This will make the executor accept no new threads
      // and finish all existing threads in the queue
      executor.shutdown();
      // Wait until all threads are finish
      while (!executor.isTerminated()) {
      }
      Set<Integer> set = new HashSet<Integer>();
      for (Future<Integer> future : list) {
        try {
          set.add(future.get());
        } catch (InterruptedException e) {
          e.printStackTrace();
        } catch (ExecutionException e) {
          e.printStackTrace();
        }
      }
      if (list.size()!=set.size()){
        throw new RuntimeException("Double-entries!!!"); 
      }

    }


}