import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadPoolExecutor;
  
public class CallableExample 
{
      public static void main(String[] args) 
      {
          ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(4);
            
          List<Future<Integer>> resultList = new ArrayList<>();
            
          Random random = new Random();
            
          for (int i=0; i<10; i++)
          {
              Integer number = random.nextInt(100);
              FactorialCalculator calculator  = new FactorialCalculator(number);
              Future<Integer> result = executor.submit(calculator);
              resultList.add(result);
          }
            
          for(Future<Integer> future : resultList)
          {
                try
                {
                    System.out.println("Future result is - " + " - " + future.get() + "; And Task done is " + future.isDone());
                } 
                catch (InterruptedException | ExecutionException e) 
                {
                    e.printStackTrace();
                }
            }
            //shut down the executor service now
            executor.shutdown();
      }
}
 
 
 
 
 
 
 
 
import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;
 
class FactorialCalculator implements Callable<Integer>
{
  
    private Integer number;
  
    public FactorialCalculator(Integer number) {
        this.number = number;
    }
  
    @Override
    public Integer call() throws Exception {
      int i = 0;
        while(!Thread.terminated()) {
          i++;
        }
        return i;
    }
}