Java in a Nutshell, 5th Edition

Name

Future<V>

Synopsis

This interface represents the result of a computation that may not be available until some time in the future. Future is a generic type, with a type variable V. V represents the type of the future value to be returned by the get( ) method. A Future<V> value is typically obtained by submitting a Callable<V> to an ExecutorService for asynchronous execution.

The key method of the Future interface is get( ). It returns the result (of type V) of the computation, blocking, if necessary, until that result is ready. get( ) throws a CancellationException if the computation is canceled with the cancel( ) method before it completes. If the computation throws an exception of its own (as the Callable.call( ) method can), get( ) throws an ExecutionException wrapped around that exception. Additionally, the timed version of the get( ) method throws a TimeoutException if the timeout elapses before the computation completes.

As noted above, the computation represented by a Future object can be canceled by calling its cancel( ) method. This method returns true if the computation was canceled successfully, and false otherwise. If you pass false to cancel( ), any computation that has started running is allowed to complete. In this case, only computations that have not yet started can be canceled. If you pass true to the cancel( ) method, running computations are interrupted with Thread.interrupt( ). Note, however, that interrupting a thread does not guarantee that it will stop running. ...