Future

public interface Future

Known Indirect Subclasses CompletableFuture<T>, CountedCompleter<T>, ForkJoinTask<V>, FutureTask<V>, RecursiveAction, RecursiveTask<V>, RunnableFuture<V>, RunnableScheduledFuture<V>, ScheduledFuture<V> CompletableFuture<T> A Future that may be explicitly completed (setting its value and status), and may be used as a CompletionStage, supporting dependent functions and actions that trigger upon its completion.  CountedCompleter<T> A ForkJoinTask with a completion action performed when triggered and there are no remaining pending actions.  ForkJoinTask<V> Abstract base class for tasks that run within a ForkJoinPool.  FutureTask<V> A cancellable asynchronous computation.  RecursiveAction A recursive resultless ForkJoinTask.  RecursiveTask<V> A recursive result-bearing ForkJoinTask.  RunnableFuture<V> A Future that is Runnable.  RunnableScheduledFuture<V> A ScheduledFuture that is Runnable.  ScheduledFuture<V> A delayed result-bearing action that can be cancelled.

A Future represents the result of an asynchronous computation. Methods are provided to check if the computation is complete, to wait for its completion, and to retrieve the result of the computation. The result can only be retrieved using method get when the computation has completed, blocking if necessary until it is ready. Cancellation is performed by the cancel method. Additional methods are provided to determine if the task completed normally or was cancelled. Once a computation has completed, the computation cannot be cancelled. If you would like to use a Future for the sake of cancellability but not provide a usable result, you can declare types of the form Future<?> and return null as a result of the underlying task.

Sample Usage (Note that the following classes are all made-up.)

 interface ArchiveSearcher { String search(String target); }
 class App {
   ExecutorService executor = ...
   ArchiveSearcher searcher = ...
   void showSearch(final String target)
       throws InterruptedException {
     Future<String> future
       = executor.submit(new Callable<String>() {
         public String call() {
             return searcher.search(target);
         }});
     displayOtherThings(); // do other things while searching
     try {
       displayText(future.get()); // use future
     } catch (ExecutionException ex) { cleanup(); return; }
   }
 }

 FutureTask<String> future =
   new FutureTask<>(new Callable<String>() {
     public String call() {
       return searcher.search(target);
   }});
 executor.execute(future);

Memory consistency effects: Actions taken by the asynchronous computation happen-before actions following the corresponding Future.get() in another thread.

Summary

Public methods

boolean cancel (boolean mayInterruptIfRunning)

V get (long timeout, 
                TimeUnit unit)

V get ()

boolean isCancelled ()

boolean isDone ()