W3cubDocs

Class FutureTask<V>

java.lang.Object

java.util.concurrent.FutureTask<V>

Type Parameters:: V - The result type returned by this FutureTask's get methods

All Implemented Interfaces:: Runnable, Future<V>, RunnableFuture<V>

public class FutureTask<V> extends Object implements RunnableFuture<V>

A cancellable asynchronous computation. This class provides a base implementation of Future, with methods to start and cancel a computation, query to see if the computation is complete, and retrieve the result of the computation. The result can only be retrieved when the computation has completed; the get methods will block if the computation has not yet completed. Once the computation has completed, the computation cannot be restarted or cancelled (unless the computation is invoked using runAndReset()).

A FutureTask can be used to wrap a Callable or Runnable object. Because FutureTask implements Runnable, a FutureTask can be submitted to an Executor for execution.

In addition to serving as a standalone class, this class provides protected functionality that may be useful when creating customized task classes.

Since:: 1.5

Nested Class Summary

Nested classes/interfaces declared in interface java.util.concurrent.Future

Future.State

Constructor Summary

Constructor	Description
`FutureTask(Runnable runnable, V result)`	Creates a `FutureTask` that will, upon running, execute the given `Runnable`, and arrange that `get` will return the given result on successful completion.
`FutureTask(Callable<V> callable)`	Creates a `FutureTask` that will, upon running, execute the given `Callable`.

Method Summary

Modifier and Type	Method	Description
`boolean`	`cancel(boolean mayInterruptIfRunning)`	Attempts to cancel execution of this task.
`protected void`	`done()`	Protected method invoked when this task transitions to state `isDone` (whether normally or via cancellation).
`V`	`get()`	Waits if necessary for the computation to complete, and then retrieves its result.
`V`	`get(long timeout, 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()`	Returns `true` if this task was cancelled before it completed normally.
`boolean`	`isDone()`	Returns `true` if this task completed.
`void`	`run()`	Sets this Future to the result of its computation unless it has been cancelled.
`protected boolean`	`runAndReset()`	Executes the computation without setting its result, and then resets this future to initial state, failing to do so if the computation encounters an exception or is cancelled.
`protected void`	`set(V v)`	Sets the result of this future to the given value unless this future has already been set or has been cancelled.
`protected void`	`setException(Throwable t)`	Causes this future to report an `ExecutionException` with the given throwable as its cause, unless this future has already been set or has been cancelled.
`String`	`toString()`	Returns a string representation of this FutureTask.

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods declared in interface java.util.concurrent.Future

exceptionNow, resultNow, state

Constructor Details

FutureTask

public FutureTask(Callable<V> callable)

Creates a FutureTask that will, upon running, execute the given Callable.

Parameters:: callable - the callable task
Throws:: NullPointerException - if the callable is null

FutureTask

public FutureTask(Runnable runnable, V result)

Creates a FutureTask that will, upon running, execute the given Runnable, and arrange that get will return the given result on successful completion.

Parameters:: runnable - the runnable task; result - the result to return on successful completion. If you don't need a particular result, consider using constructions of the form: Future<?> f = new FutureTask<Void>(runnable, null)
Throws:: NullPointerException - if the runnable is null