JavaTM 2 Platform Std. Ed. v1.6.0
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<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.
- 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 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)
- 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
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, 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 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 waitunit - 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
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
Copyright 2003 Sun Microsystems, Inc. All rights reserved
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