FutureTask

public class FutureTask 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.

Public Constructor Summary

FutureTask(Callable<V> callable)
Creates a FutureTask that will, upon running, execute the given Callable.
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.

Public Method Summary

boolean
cancel(boolean mayInterruptIfRunning)
Attempts to cancel execution of this task.
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.
V
get()
Waits if necessary for the computation to complete, and then retrieves its result.
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 Method Summary

void
done()
Protected method invoked when this task transitions to state isDone (whether normally or via cancellation).
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.
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.
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.

Inherited Method Summary

Public Constructors

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

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