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
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 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.
Summary
Public Constructors
Public Methods
Protected Methods
clone,
equals,
finalize,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait
Details
Public Constructors
public
FutureTask(Callable<V> callable)
Creates a
FutureTask that will upon running, execute the
given
Callable.
Parameters
callable
| the callable task |
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<Object>(runnable, null) |
Public Methods
public
boolean
cancel(boolean mayInterruptIfRunning)
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.
public
V
get()
Waits if necessary for the computation to complete, and then
retrieves its result.
public
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.
public
boolean
isCancelled()
Returns true if this task was cancelled before it completed
normally.
public
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.
public
void
run()
Sets this Future to the result of computation unless
it has been cancelled.
Protected Methods
protected
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.
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
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.