FutureTask (Java 2 Platform SE 5.0) (original) (raw)

java.util.concurrent

Class FutureTask

java.lang.Object extended by java.util.concurrent.FutureTask

Type Parameters:

V - The result type returned by this FutureTask's get method

All Implemented Interfaces:

Runnable, Future

public class FutureTask

extends Object

implements Future, Runnable

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 method will block if the computation has not yet completed. Once the computation has completed, the computation cannot be restarted or cancelled.

A FutureTask can be used to wrap a Callable orRunnable 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 providesprotected functionality that may be useful when creating customized task classes.

Since:

1.5

Constructor Summary
FutureTask(Callable<V> callable) Creates a FutureTask that will upon running, execute the given Callable.
[FutureTask](../../../java/util/concurrent/FutureTask.html#FutureTask%28java.lang.Runnable, V%29)(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.

Method Summary
boolean	cancel(boolean mayInterruptIfRunning) Attempts to cancel execution of this task.
protected void	done() Protected method invoked when this task transitions to stateisDone (whether normally or via cancellation).
V	get() Waits if necessary for the computation to complete, and then retrieves its result.
V	[get](../../../java/util/concurrent/FutureTask.html#get%28long, java.util.concurrent.TimeUnit%29)(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 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.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, [wait](../../../java/lang/Object.html#wait%28long, int%29)

Constructor Detail

FutureTask

public FutureTask(Callable<V> callable)

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

Parameters:

callable - the callable task

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if 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(runnable, null)

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if runnable is null

Method Detail

isCancelled

public boolean isCancelled()

Description copied from interface: [Future](../../../java/util/concurrent/Future.html#isCancelled%28%29)

Returns true if this task was cancelled before it completed normally.

Specified by:

[isCancelled](../../../java/util/concurrent/Future.html#isCancelled%28%29) in interface [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/FutureTask.html "type parameter in FutureTask")>

Returns:

true if task was cancelled before it completed

isDone

public boolean isDone()

Description copied from interface: [Future](../../../java/util/concurrent/Future.html#isDone%28%29)

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 returntrue.

Specified by:

[isDone](../../../java/util/concurrent/Future.html#isDone%28%29) in interface [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/FutureTask.html "type parameter in FutureTask")>

Returns:

true if this task completed.

cancel

public boolean cancel(boolean mayInterruptIfRunning)

Description copied from interface: [Future](../../../java/util/concurrent/Future.html#cancel%28boolean%29)

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.

Specified by:

[cancel](../../../java/util/concurrent/Future.html#cancel%28boolean%29) in interface [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/FutureTask.html "type parameter in FutureTask")>

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

get

public V get() throws InterruptedException, ExecutionException

Description copied from interface: [Future](../../../java/util/concurrent/Future.html#get%28%29)

Waits if necessary for the computation to complete, and then retrieves its result.

Specified by:

[get](../../../java/util/concurrent/Future.html#get%28%29) in interface [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/FutureTask.html "type parameter in FutureTask")>

Returns:

the computed result

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if the current thread was interrupted while waiting

[ExecutionException](../../../java/util/concurrent/ExecutionException.html "class in java.util.concurrent") - if the computation threw an exception

get

public V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException

Description copied from interface: [Future](../../../java/util/concurrent/Future.html#get%28long, java.util.concurrent.TimeUnit%29)

Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.

Specified by:

[get](../../../java/util/concurrent/Future.html#get%28long, java.util.concurrent.TimeUnit%29) in interface [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/FutureTask.html "type parameter in FutureTask")>

Parameters:

timeout - the maximum time to wait

unit - the time unit of the timeout argument

Returns:

the computed result

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if the current thread was interrupted while waiting

[ExecutionException](../../../java/util/concurrent/ExecutionException.html "class in java.util.concurrent") - if the computation threw an exception

[TimeoutException](../../../java/util/concurrent/TimeoutException.html "class in java.util.concurrent") - if the wait timed out

done

protected void done()

Protected method invoked when this task transitions to stateisDone (whether normally or via cancellation). The default implementation does nothing. Subclasses may override this method to invoke completion callbacks or perform bookkeeping. Note that you can query status inside the implementation of this method to determine whether this task has been cancelled.

set

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.

Parameters:

v - the value

setException

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.

Parameters:

t - the cause of failure.

run

public void run()

Sets this Future to the result of computation unless it has been cancelled.

Specified by:

[run](../../../java/lang/Runnable.html#run%28%29) in interface [Runnable](../../../java/lang/Runnable.html "interface in java.lang")

See Also:

Thread.run()

runAndReset

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. This is designed for use with tasks that intrinsically execute more than once.

Returns:

true if successfully run and reset

Submit a bug or feature
For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.