13. Callable and Future

Java Multithreading: Callable and Future

How to use Callable and Future in Java to get results from your threads and to allow your threads to throw exceptions. Plus, Future allows you to control your threads, checking to see if they’re running or not, waiting for results and even interrupting them or descheduling them.

Code For This Tutorial

import java.io.IOException;

import java.util.Random;

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 App {

    public static void main(String[] args) {

        ExecutorService executor = Executors.newCachedThreadPool();

        

        Future<Integer> future = executor.submit(new Callable<Integer>() {

            @Override

            public Integer call() throws Exception {

                Random random = new Random();

                int duration = random.nextInt(4000);

                 System.out.println(duration);

                if(duration > 2000) {

                    throw new IOException("Sleeping for too long.");

                }

                

                System.out.println("Starting ...");

                

                try {

                    Thread.sleep(duration);

                } catch (InterruptedException e) {

                    // TODO Auto-generated catch block

                    e.printStackTrace();

                }

                

                System.out.println("Finished.");

                

                return duration;

            }

            

        });

        

        executor.shutdown();

        

        try {

            System.out.println("Result is: " + future.get());

        } catch (InterruptedException e) {

            e.printStackTrace();

        } catch (ExecutionException e) {

            IOException ex = (IOException) e.getCause();

            

            System.out.println(ex.getMessage());

        }

    }

}

Output:

Starting ...

Finished.

Result is: 792