Callable and ExecutorService

Callable objects is like a Runnable but the Callable object returns ability to monitor, cancel and obtain a result.

Future: A Future represents the result of an asynchronous computation. Its get() waits for the submitted task to complete and returns the result.

ExecutorService: submit method en-queues the submitted Callable and returns a Future to track its completion and obtain the result.

public class CallableDemo {
        public static void main(String...strings ){
            try {
                System.out.println(Thread.currentThread().getName());
                ExecutorService executor=new ScheduledThreadPoolExecutor(5);
                Callable<Date> callable=new Callable<Date>(){
                    @Override
                    public Date call() throws Exception {
                        System.out.println(Thread.currentThread().getName());
                        return new Date();                        
                    }
                };
                Future<Date> fDate=executor.submit(callable);
                System.out.println(fDate.get());
            } catch (Exception e) {}
        }
}

FutureTask- Lets you run a Callable impl to directly run on a thread, instead of submitting to a ExecutorService.

FutureTask task=new FutureTask(new CallableImpl());
Thread t1=new Thread(task);
t1.start();
while(!task.isDone());
task.get();  //get the result