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java.util.concurrent
Class FutureTask<V>
java.lang.Object
java.util.concurrent.FutureTask<V>
-
-
Type Parameters:
-
V - The result type returned by this FutureTask's
get
method
-
All Implemented Interfaces:
-
Runnable
,
Future
<V>,
RunnableFuture
<V>
-
public class FutureTask<V>
- extends Object
- implements
RunnableFuture![](../../../diffpics/oold.gif)
Future
<V> ![](../../../diffpics/oold.gif)
<V>, ![](../../../diffpics/oold.gif)
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
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
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. |
Method Summary
|
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. |
Methods inherited from class java.lang.
Object
|
clone
,
equals
,
finalize
,
getClass
,
hashCode
,
notify
,
notifyAll
,
toString
,
wait
,
wait
,
wait
|
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 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<Object>(runnable, null)
-
Throws:
-
NullPointerException
- if runnable is null
isCancelled
public boolean isCancelled()
-
Description copied from interface:
Future
-
Returns
true
if this task was cancelled before it completed normally.
-
-
Specified by:
-
isCancelled
in interface
Future
<
V
>
-
-
Returns:
-
true
if
this
task was cancelled before it completed
isDone
public boolean isDone()
-
Description copied from interface:
Future
-
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
.
-
-
Specified by:
-
isDone
in interface
Future
<
V
>
-
-
Returns:
-
true
if this task
completed
completed.
cancel
public boolean cancel(boolean mayInterruptIfRunning)
-
Description copied from interface:
Future
-
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.
After this method returns, subsequent calls to
Future.isDone()
will always return
true
. Subsequent calls to
Future.isCancelled()
will always return
true
if this method returned
true
.
-
-
Specified by:
-
cancel
in interface
Future
<
V
>
-
-
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
-
Waits if necessary for the computation to complete, and then retrieves its result.
-
-
Specified by:
-
get
in interface
Future
<
V
>
-
-
Returns:
-
the computed result
-
Throws:
-
CancellationException
- if the computation was cancelled
-
InterruptedException
- if the current thread was interrupted while waiting
-
ExecutionException
- if the computation threw an exception
get
public V get(long timeout,
TimeUnit unit)
throws InterruptedException,
ExecutionException,
TimeoutException
-
Description copied from interface:
Future
-
Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.
-
-
Specified by:
-
get
in interface
Future
<
V
>
-
-
Parameters:
-
timeout - the maximum time to wait
-
unit - the time unit of the timeout argument
-
Returns:
-
the computed result
-
Throws:
-
CancellationException
- if the computation was cancelled
-
InterruptedException
- if the current thread was interrupted while waiting
-
ExecutionException
- if the computation threw an exception
-
TimeoutException
- if the wait timed out
done
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.
-
-
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.
This method is invoked internally by the
run
method upon successful completion of the computation.
-
-
-
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.
This method is invoked internally by the
run
method upon failure of the computation.
-
-
-
Parameters:
-
t - the cause of
failure
failure.
run
public void run()
-
Sets this Future to the result of
its
computation unless it has been cancelled.
-
-
Specified by:
-
run
in interface
Runnable
-
Specified by:
-
run
in interface
RunnableFuture
<
V
>
-
-
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