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FlexDoc/Javadoc 2.0 Demo Java Doc |
Class FutureTask<V>
java.util.concurrent.FutureTask<V>
Type Parameters:
V - The result type returned by this FutureTask's
get methods
All Implemented Interfaces:
public class 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.
Since:
1.5
Author:
Doug Lea
Constructor Summary |
Creates a FutureTask that will, upon running, execute the
given Callable.
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Creates a FutureTask that will, upon running, execute the
given Runnable, and arrange that get will return the
given result on successful completion.
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Method Summary |
boolean |
cancel(boolean mayInterruptIfRunning)
Attempts to cancel execution of this task.
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protected void |
Protected method invoked when this task transitions to state
isDone (whether normally or via cancellation).
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Waits if necessary for the computation to complete, and then
retrieves its result.
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Waits if necessary for at most the given time for the computation
to complete, and then retrieves its result, if available.
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boolean |
Returns true if this task was cancelled before it completed
normally.
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boolean |
Returns true if this task completed.
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void |
Sets this Future to the result of its computation
unless it has been cancelled.
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protected boolean |
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.
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protected void |
Sets the result of this future to the given value unless
this future has already been set or has been cancelled.
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protected void |
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.
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Returns a string representation of this FutureTask.
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Methods inherited from class java.lang. Object |
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Creates a
FutureTask that will, upon running, execute the
given
Callable.
Parameters:
callable - the callable task
Throws:
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<Void>(runnable, null)
Throws:
public boolean isCancelled |
() |
Description copied from interface:
Future
Returns true if this task was cancelled before it completed
normally.
Specified by:
Returns:
true if this task was cancelled before it completed
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:
Returns:
true if this task completed
public boolean cancel |
(boolean mayInterruptIfRunning) |
Description copied from interface:
Future
Attempts to cancel execution of this task. This method has no
effect if the task is already completed or cancelled, or could
not be cancelled for some other reason. Otherwise, if 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 (when known by the implementation)
is interrupted in an attempt to stop the task.
The return value from this method does not necessarily
indicate whether the task is now cancelled; use Future.isCancelled().
Specified by:
Parameters:
mayInterruptIfRunning - true if the thread
executing this task should be interrupted (if the thread is
known to the implementation); otherwise, in-progress tasks are
allowed to complete
Returns:
false if the task could not be cancelled,
typically because it has already completed; true
otherwise. If two or more threads cause a task to be cancelled,
then at least one of them returns true. Implementations
may provide stronger guarantees.
Description copied from interface:
Future
Waits if necessary for the computation to complete, and then
retrieves its result.
Specified by:
Returns:
the computed result
Throws:
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:
Parameters:
timeout - the maximum time to wait
unit - the time unit of the timeout argument
Returns:
the computed result
Throws:
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.
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
protected void setException |
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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
Sets this Future to the result of its computation
unless it has been cancelled.
Specified by:
See Also:
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
Returns a string representation of this FutureTask.
Implementation Requirements:
The default implementation returns a string identifying this
FutureTask, as well as its completion state. The state, in
brackets, contains one of the strings "Completed Normally",
"Completed Exceptionally", "Cancelled", or
"Not completed".
Overrides:
Returns:
a string representation of this FutureTask
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