public class FutureTask extends java.lang.Object implements RunnableFuture
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.
Constructor and Description |
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FutureTask(Callable callable)
Creates a FutureTask that will, upon running, execute the
given Callable.
|
FutureTask(java.lang.Runnable runnable,
java.lang.Object result)
Creates a FutureTask that will, upon running, execute the
given Runnable, and arrange that get will return the
given result on successful completion.
|
Modifier and Type | Method and Description |
---|---|
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).
|
java.lang.Object |
get()
Waits if necessary for the computation to complete, and then
retrieves its result.
|
java.lang.Object |
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(java.lang.Object 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(java.lang.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.
|
public FutureTask(Callable callable)
callable
- the callable taskjava.lang.NullPointerException
- if callable is nullpublic FutureTask(java.lang.Runnable runnable, java.lang.Object result)
runnable
- the runnable taskresult
- 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)java.lang.NullPointerException
- if runnable is nullpublic boolean isCancelled()
Future
isCancelled
in interface Future
public boolean isDone()
Future
public boolean cancel(boolean mayInterruptIfRunning)
Future
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.
cancel
in interface Future
mayInterruptIfRunning
- true if the thread executing this
task should be interrupted; otherwise, in-progress tasks are allowed
to completepublic java.lang.Object get() throws java.lang.InterruptedException, ExecutionException
Future
get
in interface Future
CancellationException
- if the computation was cancelledjava.lang.InterruptedException
- if the current thread was interrupted
while waitingExecutionException
- if the computation threw an
exceptionpublic java.lang.Object get(long timeout, TimeUnit unit) throws java.lang.InterruptedException, ExecutionException, TimeoutException
Future
get
in interface Future
timeout
- the maximum time to waitunit
- the time unit of the timeout argumentCancellationException
- if the computation was cancelledjava.lang.InterruptedException
- if the current thread was interrupted
while waitingExecutionException
- if the computation threw an
exceptionTimeoutException
- if the wait timed outprotected void done()
protected void set(java.lang.Object v)
v
- the valueprotected void setException(java.lang.Throwable t)
t
- the cause of failurepublic void run()
run
in interface RunnableFuture
run
in interface java.lang.Runnable
protected boolean runAndReset()