FutureTask (Java 2 Platform SE 5.0) - JDK 5 Documentation v1.5.0, Java 2 SDK 英文文档

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Standard Ed. 5.0

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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>

public class FutureTask<V>
extends Object
implements Future<V>, Runnable
extends Object
implements Future<V>, 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 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

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 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`

Constructor Detail

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

Method Detail