public
class
FutureTask
extends Object
implements
RunnableFuture<V>
| java.lang.Object | |
| ↳ | java.util.concurrent.FutureTask<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 constructors | |
|---|---|
FutureTask(Callable<V> callable)
Creates a |
|
FutureTask(Runnable runnable, V result)
Creates a |
|
Public methods | |
|---|---|
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 |
boolean
|
isDone()
Returns |
void
|
run()
Sets this Future to the result of its computation unless it has been cancelled. |
Protected methods | |
|---|---|
void
|
done()
Protected method invoked when this task transitions to state
|
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 |
Inherited methods | |
|---|---|
 From
class
java.lang.Object
| |
From
interface
java.util.concurrent.RunnableFuture
| |
From
interface
java.lang.Runnable
| |
From
interface
java.util.concurrent.Future
| |
FutureTask (Callable<V> callable)
Creates a FutureTask that will, upon running, execute the
given Callable.
| Parameters | |
|---|---|
callable |
Callable:
the callable task |
| Throws | |
|---|---|
NullPointerException |
if the callable is null |
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 |
Runnable:
the runnable task |
result |
V:
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 |
boolean cancel (boolean mayInterruptIfRunning)
Attempts to cancel execution of this task. This attempt will
fail if the task has already completed, has 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.
After this method returns, subsequent calls to isDone() will
always return true. Subsequent calls to isCancelled()
will always return true if this method returned true.
| Parameters | |
|---|---|
mayInterruptIfRunning |
boolean:
true if the thread executing this
task should be interrupted; otherwise, in-progress tasks are allowed
to complete |
| Returns | |
|---|---|
boolean |
false if the task could not be cancelled,
typically because it has already completed normally;
true otherwise
|
Developers
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.
| Parameters | |
|---|---|
timeout |
long:
the maximum time to wait |
unit |
TimeUnit:
the time unit of the timeout argument |
| Returns | |
|---|---|
V |
the computed result |
| Throws | |
|---|---|
CancellationException |
|
InterruptedException |
|
ExecutionException |
|
TimeoutException |
|
V get ()
Waits if necessary for the computation to complete, and then retrieves its result.
| Returns | |
|---|---|
V |
the computed result |
| Throws | |
|---|---|
CancellationException |
|
InterruptedException |
|
ExecutionException |
|
boolean isCancelled ()
Returns true if this task was cancelled before it completed
normally.
| Returns | |
|---|---|
boolean |
true if this task was cancelled before it completed
|
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 | |
|---|---|
boolean |
true if this task completed
|
void run ()
Sets this Future to the result of its computation unless it has been cancelled.
void done ()
Protected method invoked when this task transitions to state
isDone (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.
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 | |
|---|---|
boolean |
true if successfully run and reset
|
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.
This method is invoked internally by the run() method
upon successful completion of the computation.
| Parameters | |
|---|---|
v |
V:
the value
|
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.
This method is invoked internally by the run() method
upon failure of the computation.
| Parameters | |
|---|---|
t |
Throwable:
the cause of failure
|