How To Purpose Time To Come Too Futuretask Inward Coffee Concurrency Alongside Example

Future in addition to FutureTask inwards Java allows y'all to write asynchronous code. Future is a full general concurrency abstraction, also known equally a promise, which promises to render a effect inwards future. In asynchronous programming, primary thread doesn't aspect for whatsoever project to finished, rather it mitt over the project to workers in addition to motility on. One way of asynchronous processing is using callback methods. Future is but about other way to write asynchronous code. By using Future and FutureTask, y'all tin forcefulness out write a method which does long computation but returns immediately. Those methods, instead of returning a result, return a Future object. You tin forcefulness out after acquire the effect past times calling Future.get() method, which volition render an object of type T, where T is what Future object is holding.


One illustration of Future is submit() method of ExecutorService, which at in 1 lawsuit render a Future object. By the way, Future in addition to FutureTask are available inwards java.util.concurrent packet from Java 1.5. Also, Future is in addition to interface in addition to FutureTask is an implementation or RunnableFuture, which tin forcefulness out endure used equally a Runnable interface, thus, tin forcefulness out endure passed to ExecutorService.

In this Java concurrency tutorial, nosotros volition larn how to usage Future in addition to FutureTask inwards Java.

Future in addition to FutureTask Example - Java

One of the simplest examples of using Future is working amongst Thread pools. When y'all submit a long running project to ExecutorService, it returns a Future object immediately. This Future object tin forcefulness out endure used to query project completion in addition to getting effect of computation. In our sample Java program, nosotros convey a created a FactorialCalculator task, which wraps calculation of factorial nether Callable interface's call() method.

When nosotros submit this project amongst project of calculating factorial of a huge publish similar 100000, ExecutorService returns a Future object, which holds long value, render type of telephone yell upward method inwards our case. Later, nosotros banking concern gibe whether project is completed or non using isDone() method. From output, y'all tin forcefulness out encounter that main thread returns immediately. Since nosotros convey used get() method in 1 lawsuit project is completed, it doesn't block in addition to render effect immediately.

By the way, Future object returned past times the submit() method is also an instance of FutureTask.

Sample Java Program to usage Future in addition to FutreTask
Here is our elementary examine program, which demonstrate how y'all tin forcefulness out usage these 2 classes to produce asynchronous execution inwards Java. First nosotros convey created a FutureTask which is cipher but a nested static class which implements Callable interface. In this method nosotros telephone yell upward our factorial method to calculate factorial of a number. To brand this method long-running, nosotros convey also introduced a pocket-sized slumber duration. This volition help y'all to ameliorate empathise how Future works.

package test;  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 plan to present how to usage Future inwards Java. Future allows to write  * asynchronous code inwards Java, where Future promises effect to endure available inwards  * hereafter  *  * @author Javin  */ public class FutureDemo {      private static final ExecutorService threadpool = Executors.newFixedThreadPool(3);      public static void main(String args[]) throws InterruptedException, ExecutionException {          FactorialCalculator project = new FactorialCalculator(10);         System.out.println("Submitting Task ...");          Future hereafter = threadpool.submit(task);          System.out.println("Task is submitted");          while (!future.isDone()) {             System.out.println("Task is non completed yet....");             Thread.sleep(1); //sleep for 1 millisecond earlier checking again         }          System.out.println("Task is completed, let's banking concern gibe result");         long factorial = future.get();         System.out.println("Factorial of 1 thou m 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 endure greater than zero");             }             long effect = 1;             while (number > 0) {                 Thread.sleep(1); // adding delay for example                 effect = effect * number;                 number--;             }             return result;         }     }  }  Output Submitting Task ... Task is submitted Task is non completed yet.... Task is non completed yet.... Task is non completed yet.... Task is completed, let's banking concern gibe effect Factorial of 1 thou m is : 3628800

You tin forcefulness out encounter that because of the sleep() method nosotros convey introduced inwards factorial method, it took but about fourth dimension to halt in addition to during that fourth dimension isDone() method returned false. This is why y'all are seeing the output "Task is non completed yet". Once project is completed the effect is available equally Future object.

See Core Java for Inpatients to larn to a greater extent than virtually how to usage concurrency classes inwards Java Program.

Important points Future in addition to FutureTask  in Java

Now nosotros convey learned how to usage Future in addition to FutureTask inwards Java program. Let's revise but about primal points virtually Future concept in addition to FutureTask shape inwards Java itself.

1. Future is a base of operations interface in addition to defines abstraction of an object which promises effect to endure available inwards hereafter spell FutureTask is an implementation of the Future interface.

2. Future is a parametric interface in addition to type-safe written equally Future<V>, where V denotes value.

3. Future provides get() method to acquire result, which is blocking method in addition to blocks until effect is available to Future.

4. Future interface also defines cancel() method to cancel task.

5. isDone() in addition to isCancelled() method is used to query Future project states. isDone() returns true if project is completed in addition to effect is available to Future. If y'all telephone yell upward get() method, after isDone() returned true then it should render immediately. On the other hand, isCancelled() method returns true, if this project is cancelled earlier its completion.

6. Future has iv sub interfaces, each amongst additional functionality e.g. Response, RunnableFuture, RunnableScheduledFuture and ScheduledFuture. RunnableFuture also implements Runnable in addition to successful halt of run() method crusade completion of this Future.


7. FutureTask in addition to SwingWorker are 2 good known implementation of Future interface. FutureTask also implements RunnableFuture interface, which way this tin forcefulness out endure used equally Runnable in addition to tin forcefulness out endure submitted to ExecutorService for execution.


8. Though most of the fourth dimension ExecutorService creates FutureTask for you, i.e. when y'all submit() Callable or Runnable object. You tin forcefulness out also created it manually.


9. FutureTask is usually used to twine Runnable or Callable object in addition to submit them to ExecutorService for asynchronous execution.


That's all on How to usage Future in addition to FutureTask inwards Java. Understanding concept behind Future is rattling of import for writing asynchronous code inwards Java. In elementary words, Future allows whatsoever method to render immediately, amongst hope of effect beingness available inwards future. By using this technique your primary thread tin forcefulness out produce other things spell waiting for for certain project to endure completed.

Further Learning
Multithreading in addition to Parallel Computing inwards Java
Java Concurrency inwards Practice - The Book
Applying Concurrency in addition to Multi-threading to Common Java Patterns
Java Concurrency inwards Practice Course past times Heinz Kabutz