FutureTask

open class FutureTask<V : Any!> : 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.

Summary

Public constructors
`FutureTask(runnable: Runnable!, result: V)` 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: Callable<V>!)` Creates a `FutureTask` that will, upon running, execute the given `Callable`.

Public methods
open Boolean	`cancel(mayInterruptIfRunning: Boolean)` Attempts to cancel execution of this task.
open Throwable!	`exceptionNow()`
open V	`get()`
open V	`get(timeout: Long, unit: TimeUnit!)`
open Boolean	`isCancelled()` Returns `true` if this task was cancelled before it completed normally.
open Boolean	`isDone()` Returns `true` if this task completed.
open V	`resultNow()`
open Unit	`run()` Sets this Future to the result of its computation unless it has been cancelled.
open Future.State!	`state()`
open String	`toString()` Returns a string representation of this FutureTask.

Protected methods
open Unit	`done()` Protected method invoked when this task transitions to state `isDone` (whether normally or via cancellation).
open 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.
open Unit	`set(v: V)` Sets the result of this future to the given value unless this future has already been set or has been cancelled.
open Unit	`setException(t: Throwable!)` 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.

Public constructors

FutureTask(
    runnable: Runnable!, 
    result: V)

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`	Runnable!: the runnable task
`result`	V: 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)`

Exceptions
`java.lang.NullPointerException`	if the runnable is null

FutureTask

FutureTask(callable: Callable<V>!)

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

Parameters
`callable`	Callable<V>!: the callable task

Exceptions
`java.lang.NullPointerException`	if the callable is null

Public methods

cancel

open fun cancel(mayInterruptIfRunning: Boolean): Boolean

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 isCancelled.

Parameters
`mayInterruptIfRunning`	Boolean: `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

Return
`Boolean`	`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.

exceptionNow

open fun exceptionNow(): Throwable!

Return
`Throwable!`	the exception thrown by the task

Exceptions
`java.lang.IllegalStateException`	if the task has not completed, the task completed normally, or the task was cancelled

get

open fun get(): V

Return
`V`	the computed result

Exceptions
`java.lang.InterruptedException`	if the current thread was interrupted while waiting
`java.util.concurrent.CancellationException`	if the computation was cancelled
`java.util.concurrent.ExecutionException`	if the computation threw an exception

get

open fun get(
    timeout: Long, 
    unit: TimeUnit!
): V

Parameters
`timeout`	Long: the maximum time to wait
`unit`	TimeUnit!: the time unit of the timeout argument

Return
`V`	the computed result

Exceptions
`java.lang.InterruptedException`	if the current thread was interrupted while waiting
`java.util.concurrent.CancellationException`	if the computation was cancelled
`java.util.concurrent.ExecutionException`	if the computation threw an exception
`java.util.concurrent.TimeoutException`	if the wait timed out

isCancelled

open fun isCancelled(): Boolean

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

Return
`Boolean`	`true` if this task was cancelled before it completed

isDone

open fun isDone(): Boolean

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.

Return
`Boolean`	`true` if this task completed

resultNow

open fun resultNow(): V

Return
`V`	the computed result

Exceptions
`java.lang.IllegalStateException`	if the task has not completed or the task did not complete with a result

run

open fun run(): Unit

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

toString

open fun toString(): String

Returns a string representation of this FutureTask.

Return
`String`	a string representation of this FutureTask

Protected methods

done

protected open fun done(): Unit

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.

runAndReset

protected open fun runAndReset(): 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. This is designed for use with tasks that intrinsically execute more than once.

Return
`Boolean`	`true` if successfully run and reset

set

protected open fun set(v: V): Unit

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`	V: the value

setException

protected open fun setException(t: Throwable!): Unit

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`	Throwable!: the cause of failure

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