Asynchronous programming is very popular these days, primarily because of its ability to improve the overall throughput on a multi-core system. Asynchronous programming is a programming paradigm that facilitates fast and responsive user interfaces. The asynchronous programming model in Java provides a consistent programming model to write programs that support asynchrony.
Asynchronous programming provides a non-blocking, event-driven programming model. This programming model leverages the multiple cores in your system to provide parallelization by using multiple CPU cores to execute the tasks, thus increasing the application’s throughput. Note that throughput is a measure of the amount of work done in unit time. In this programming paradigm, a unit of work would execute separately from the main application thread and notify the calling thread about its execution state: success, in progress or failure.
Application of asynchronous can be a situation where we want to execute multiple things in parellel without waiting for 1 task to finish such that it increase the throughput of the system. Consider we want to send email to 100k+ users and at the same time need to process other data, such that we don’t want to wait for email task to complete to proceed.
Another good example of this can be logging frameworks: You typically would want to log exceptions and errors into your log targets; in other words, file, database, or something similar. There is no point for your application to wait till the logging tasks are over. In doing so, the application’s responsiveness would be affected. On the contrary, if the call to the logging framework can be made asynchronously, the application can proceed with other tasks concurrently, without having to wait. This is an example of a non-blocking mode of execution.
1. Future is a base interface and defines abstraction of an object which promises result to be available in future while FutureTask is an implementation of the Future interface.
2. Future is a parametric interface and type-safe written as Future<V>, where V denotes value.
3. Future provides get() method to get result, which is blocking method and blocks until result is available to Future.
4. Future interface also defines cancel() method to cancel task.
5. isDone() and isCancelled() method is used to query Future task states. isDone() returns true if task is completed and result is available to Future. If you call get() method, after isDone() returned true then it should return immediately. On the other hand, isCancelled() method returns true, if this task is cancelled before its completion.
6. Future has four sub interfaces, each with additional functionality e.g. Response, RunnableFuture, RunnableScheduledFuture and ScheduledFuture. RunnableFuture also implements Runnable and successful finish of run() method cause completion of this Future.
7. FutureTask and SwingWorker are two well known implementation of Future interface. FutureTask also implements RunnableFuture interface, which means this can be used as Runnable and can be submitted to ExecutorService for execution.
8. Though most of the time ExecutorService creates FutureTask for you, i.e. when you submit() Callable or Runnable object. You can also created it manually.
9. FutureTask is normally used to wrap Runnable or Callable object and submit them to ExecutorService for asynchronous execution.
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;
import java.util.logging.Level;
import java.util.logging.Logger; /** * Java program to show how to use Future in Java. Future allows to write * asynchronous code in Java, where Future promises result to be available in * future * * @author Javin */
public class FutureDemo {
private static final ExecutorService threadpool = Executors.newFixedThreadPool(2);
public static void main(String args[]) throws InterruptedException, ExecutionException {
FactorialCalculator task = new FactorialCalculator(1000);
System.out.println(“Submitting Task …”);
Future future = threadpool.submit(task);
System.out.println(“Task is submitted”);
while (!future.isDone()) {
System.out.println(“Task is not completed yet….”);
Thread.sleep(1); //sleep for 1 millisecond before checking again
}
System.out.println(“Task is completed, let’s check result”);
long factorial = (long) future.get();
System.out.println(“Factorial of 1000000 is : ” + factorial);
threadpool.shutdown();
}
private static class FactorialCalculator implements Callable {
private final int number;
public FactorialCalculator(int number) {
this.number = number;
}
@Override public Long call() {
long output = 0;
try {
output = factorial(number);
} catch (InterruptedException ex) {
//Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
}
return output;
}
private long factorial(int number) throws InterruptedException {
if (number < 0) {
throw new IllegalArgumentException(“Number must be greater than zero”);
}
long result = 1;
while (number > 0) {
Thread.sleep(1); // adding delay for example
result = result * number;
number–;
}
return result;
}
}
}
Bhavesh Gadoya 
Thanks, nice post