java.util.concurrent
class FutureTask

java.lang.Object java.util.concurrent.FutureTask

All Implemented Interfaces:

RunnableFuture

public class FutureTask
extends Object
implements RunnableFuture

A cancellable asynchronous computation. This class provides a base implementation of {@link 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 {@link Callable} or {@link java.lang.Runnable} object. Because FutureTask implements Runnable, a FutureTask can be submitted to an {@link 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.

FutureTask

public FutureTask(Callable callable)

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

Parameters:

callable - the callable task

FutureTask

public FutureTask(Runnable runnable,
                  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.

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)

cancel

public boolean cancel(boolean mayInterruptIfRunning)

Parameters:

mayInterruptIfRunning

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.

get

public Object get()
           throws InterruptedException,
                  ExecutionException

Throws:

InterruptedException

ExecutionException

get

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

Parameters:

timeout

unit

Throws:

InterruptedException

ExecutionException

TimeoutException

isCancelled

public boolean isCancelled()

isDone

public boolean isDone()

run

public void run()

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

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

set

protected void set(Object 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