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 |
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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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Creates a FutureTask that will, upon running, execute the given Callable.
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| Protected methods |
| open Unit |
Protected method invoked when this task transitions to state isDone (whether normally or via cancellation).
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| open 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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| open Unit |
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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| open 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.
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Public constructors
FutureTask
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
| 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.util.concurrent.CancellationException |
if the computation was cancelled |
java.util.concurrent.ExecutionException |
if the computation threw an exception |
java.lang.InterruptedException |
if the current thread was interrupted while waiting |
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.util.concurrent.CancellationException |
if the computation was cancelled |
java.util.concurrent.ExecutionException |
if the computation threw an exception |
java.lang.InterruptedException |
if the current thread was interrupted while waiting |
java.util.concurrent.TimeoutException |
if the wait timed out |
isCancelled
open fun isCancelled(): Boolean
| Return |
Boolean |
true if this task was cancelled before it completed |
isDone
open fun isDone(): Boolean
| 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 |
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 |
