Callable and Future in Java

Java Programming Java8Object Oriented Programming

java.util.concurrent.The callable object can return the computed result done by a thread in contrast to a runnable interface which can only run the thread. The Callable object returns a Future object which provides methods to monitor the progress of a task being executed by a thread. The future object can be used to check the status of a Callable and then retrieve the result from the Callable once the thread is done. It also provides timeout functionality.

Syntax

//submit the callable using ThreadExecutor
//and get the result as a Future object
Future<Long> result10 = executor.submit(new FactorialService(10));  

//get the result using get method of the Future object
//get method waits till the thread execution and then return the result of the execution.
Long factorial10 = result10.get();

Example

The following TestThread program shows usage of Futures and Callables in the thread based environment.

Live Demo

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 TestThread {

   public static void main(final String[] arguments) throws InterruptedException, ExecutionException {

      ExecutorService executor = Executors.newSingleThreadExecutor();

      System.out.println("Factorial Service called for 10!");
      Future<Long> result10 = executor.submit(new FactorialService(10));

      System.out.println("Factorial Service called for 20!");
      Future<Long> result20 = executor.submit(new FactorialService(20));

      Long factorial10 = result10.get();
      System.out.println("10! = " + factorial10);

      Long factorial20 = result20.get();
      System.out.println("20! = " + factorial20);

      executor.shutdown();
   }  

   static class FactorialService implements Callable<Long> {
      private int number;

      public FactorialService(int number) {
         this.number = number;
      }

      @Override
      public Long call() throws Exception {
         return factorial();
      }

      private Long factorial() throws InterruptedException {
         long result = 1;
                   
         while (number != 0) {              
            result = number * result;
            number--;
            Thread.sleep(100);          
         }
         return result;      
      }
   }
}

This will produce the following result.

Output

Factorial Service called for 10!
Factorial Service called for 20!
10! = 3628800
20! = 2432902008176640000
raja
Published on 20-Jul-2018 13:02:55
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