程序包 java.util.concurrent

类 FutureTask<V>

java.lang.Object

java.util.concurrent.FutureTask<V>

类型参数:

V - The result type returned by this FutureTask's get methods

所有已实现的接口:

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 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.

从以下版本开始:

1.5

构造器概要

构造器

构造器	说明
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.
FutureTask(Callable<V> callable)	Creates a FutureTask that will, upon running, execute the given Callable.

方法概要

限定符和类型	方法	说明
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.

从类继承的方法 java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

构造器详细资料

FutureTask

public FutureTask(Callable<V> callable)

Creates a FutureTask that will, upon running, execute the given Callable.

参数:

callable - the callable task

抛出:

NullPointerException - if the 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.

参数:

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)

抛出:

NullPointerException - if the runnable is null

方法详细资料

isCancelled

public boolean isCancelled()

从接口复制的说明: Future

Returns true if this task was cancelled before it completed normally.

指定者:

isCancelled 在接口中 Future<V>

返回:

true if this task was cancelled before it completed

isDone

public boolean isDone()

从接口复制的说明: 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.

指定者:

isDone 在接口中 Future<V>

返回:

true if this task completed

cancel

public boolean cancel(boolean mayInterruptIfRunning)

从接口复制的说明: 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.

指定者:

cancel 在接口中 Future<V>

参数:

mayInterruptIfRunning - true if the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete

返回:

false if the task could not be cancelled, typically because it has already completed normally; true otherwise

get

public V get()
      throws ExecutionException,
             InterruptedException

从接口复制的说明: Future

Waits if necessary for the computation to complete, and then retrieves its result.

指定者:

get 在接口中 Future<V>

返回:

the computed result

抛出:

CancellationException - if the computation was cancelled

ExecutionException - if the computation threw an exception

InterruptedException - if the current thread was interrupted while waiting

get

public V get(long timeout,
             TimeUnit unit)
      throws ExecutionException,
             InterruptedException,
             TimeoutException

从接口复制的说明: Future

Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.

指定者:

get 在接口中 Future<V>

参数:

timeout - the maximum time to wait

unit - the time unit of the timeout argument

返回:

the computed result

抛出:

CancellationException - if the computation was cancelled

ExecutionException - if the computation threw an exception

InterruptedException - if the current thread was interrupted while waiting

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.

参数:

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.

参数:

t - the cause of failure

run

public void run()

从接口复制的说明: RunnableFuture

Sets this Future to the result of its computation unless it has been cancelled.

指定者:

run 在接口中 Runnable

指定者:

run 在接口中 RunnableFuture<V>

另请参阅:

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.

返回:

true if successfully run and reset