java.util.concurrent
Interface Future<V>

Type Parameters:
V - The result type returned by this Future's get method
All Known Subinterfaces:
ScheduledFuture sample code for java.util.concurrent.ScheduledFuture definition code for java.util.concurrent.ScheduledFuture <V>
All Known Implementing Classes:
FutureTask sample code for java.util.concurrent.FutureTask definition code for java.util.concurrent.FutureTask

public interface Future<V>

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; }
   }
 }
 
The FutureTask sample code for java.util.concurrent.FutureTask definition code for java.util.concurrent.FutureTask class is an implementation of Future that implements Runnable, and so may be executed by an Executor. For example, the above construction with submit could be replaced by:
     FutureTask<String> future =
       new FutureTask<String>(new Callable<String>() {
         public String call() {
           return searcher.search(target);
       }});
     executor.execute(future);
 

Since:
1.5
See Also:
FutureTask sample code for java.util.concurrent.FutureTask definition code for java.util.concurrent.FutureTask , Executor sample code for java.util.concurrent.Executor definition code for java.util.concurrent.Executor

Method Summary
 boolean cancel sample code for java.util.concurrent.Future.cancel(boolean) definition code for java.util.concurrent.Future.cancel(boolean) (boolean mayInterruptIfRunning)
          Attempts to cancel execution of this task.
 V get sample code for java.util.concurrent.Future.get() definition code for java.util.concurrent.Future.get() ()
          Waits if necessary for the computation to complete, and then retrieves its result.
 V get sample code for java.util.concurrent.Future.get(long, java.util.concurrent.TimeUnit) definition code for java.util.concurrent.Future.get(long, java.util.concurrent.TimeUnit) (long timeout, TimeUnit sample code for java.util.concurrent.TimeUnit definition code for java.util.concurrent.TimeUnit  unit)
          Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.
 boolean isCancelled sample code for java.util.concurrent.Future.isCancelled() definition code for java.util.concurrent.Future.isCancelled() ()
          Returns true if this task was cancelled before it completed normally.
 boolean isDone sample code for java.util.concurrent.Future.isDone() definition code for java.util.concurrent.Future.isDone() ()
          Returns true if this task completed.
 

Method Detail

cancel sample code for java.util.concurrent.Future.cancel(boolean) definition code for java.util.concurrent.Future.cancel(boolean)

boolean cancel(boolean mayInterruptIfRunning)
Attempts to cancel execution of this task. This attempt will fail if the task has already completed, already been cancelled, or could not be cancelled for some other reason. If successful, and this task has not started when cancel is called, this task should never run. If the task has already started, then the mayInterruptIfRunning parameter determines whether the thread executing this task should be interrupted in an attempt to stop the task.

Parameters:
mayInterruptIfRunning - true if the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete
Returns:
false if the task could not be cancelled, typically because it has already completed normally; true otherwise

isCancelled sample code for java.util.concurrent.Future.isCancelled() definition code for java.util.concurrent.Future.isCancelled()

boolean isCancelled()
Returns true if this task was cancelled before it completed normally.

Returns:
true if task was cancelled before it completed

isDone sample code for java.util.concurrent.Future.isDone() definition code for java.util.concurrent.Future.isDone()

boolean isDone()
Returns true if this task completed. Completion may be due to normal termination, an exception, or cancellation -- in all of these cases, this method will return true.

Returns:
true if this task completed.

get sample code for java.util.concurrent.Future.get() definition code for java.util.concurrent.Future.get()

V get()
      throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException ,
             ExecutionException sample code for java.util.concurrent.ExecutionException definition code for java.util.concurrent.ExecutionException 
Waits if necessary for the computation to complete, and then retrieves its result.

Returns:
the computed result
Throws:
CancellationException sample code for java.util.concurrent.CancellationException definition code for java.util.concurrent.CancellationException - if the computation was cancelled
ExecutionException sample code for java.util.concurrent.ExecutionException definition code for java.util.concurrent.ExecutionException - if the computation threw an exception
InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if the current thread was interrupted while waiting

get sample code for java.util.concurrent.Future.get(long, java.util.concurrent.TimeUnit) definition code for java.util.concurrent.Future.get(long, java.util.concurrent.TimeUnit)

V get(long timeout,
      TimeUnit sample code for java.util.concurrent.TimeUnit definition code for java.util.concurrent.TimeUnit  unit)
      throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException ,
             ExecutionException sample code for java.util.concurrent.ExecutionException definition code for java.util.concurrent.ExecutionException ,
             TimeoutException sample code for java.util.concurrent.TimeoutException definition code for java.util.concurrent.TimeoutException 
Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.

Parameters:
timeout - the maximum time to wait
unit - the time unit of the timeout argument
Returns:
the computed result
Throws:
CancellationException sample code for java.util.concurrent.CancellationException definition code for java.util.concurrent.CancellationException - if the computation was cancelled
ExecutionException sample code for java.util.concurrent.ExecutionException definition code for java.util.concurrent.ExecutionException - if the computation threw an exception
InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if the current thread was interrupted while waiting
TimeoutException sample code for java.util.concurrent.TimeoutException definition code for java.util.concurrent.TimeoutException - if the wait timed out