Future (Java SE 9 & JDK 9 ) (original) (raw)
- Type Parameters:
V
- The result type returned by this Future'sget
method
All Known Subinterfaces:[Response](../../../javax/xml/ws/Response.html "interface in javax.xml.ws")<T>
,[RunnableFuture](../../../java/util/concurrent/RunnableFuture.html "interface in java.util.concurrent")<V>
,[RunnableScheduledFuture](../../../java/util/concurrent/RunnableScheduledFuture.html "interface in java.util.concurrent")<V>
,[ScheduledFuture](../../../java/util/concurrent/ScheduledFuture.html "interface in java.util.concurrent")<V>
All Known Implementing Classes:[CompletableFuture](../../../java/util/concurrent/CompletableFuture.html "class in java.util.concurrent")
,[CountedCompleter](../../../java/util/concurrent/CountedCompleter.html "class in java.util.concurrent")
,[ForkJoinTask](../../../java/util/concurrent/ForkJoinTask.html "class in java.util.concurrent")
,[FutureTask](../../../java/util/concurrent/FutureTask.html "class in java.util.concurrent")
,[RecursiveAction](../../../java/util/concurrent/RecursiveAction.html "class in java.util.concurrent")
,[RecursiveTask](../../../java/util/concurrent/RecursiveTask.html "class in java.util.concurrent")
,[SwingWorker](../../../javax/swing/SwingWorker.html "class in javax.swing")
,[Task](../../../javafx/concurrent/Task.html "class in javafx.concurrent")
public interface Future
A Future
represents the result of an asynchronous computation. Methods are provided to check if the computation is complete, to wait for its completion, and to retrieve the result of the computation. The result can only be retrieved using methodget
when the computation has completed, blocking if necessary until it is ready. Cancellation is performed by thecancel
method. Additional methods are provided to determine if the task completed normally or was cancelled. Once a computation has completed, the computation cannot be cancelled. If you would like to use a Future
for the sake of cancellability but not provide a usable result, you can declare types of the form Future<?>
and return null
as a result of the underlying task.
Sample Usage (Note that the following classes are all made-up.)
interface ArchiveSearcher { String search(String target); } class App { ExecutorService executor = ... ArchiveSearcher searcher = ... void showSearch(String target) throws InterruptedException { Callable<String> task = () -> searcher.search(target); Future<String> future = executor.submit(task); displayOtherThings(); // do other things while searching try { displayText(future.get()); // use future } catch (ExecutionException ex) { cleanup(); return; } } }
The FutureTask class is an implementation of Future
that implements Runnable
, and so may be executed by an Executor
. For example, the above construction with submit
could be replaced by:
FutureTask<String> future = new FutureTask<>(task); executor.execute(future);
Memory consistency effects: Actions taken by the asynchronous computation happen-before actions following the corresponding Future.get()
in another thread.
Since:
1.5
See Also:
FutureTask, Executor
Method Summary
All Methods Instance Methods Abstract Methods
Modifier and Type Method Description boolean cancel(boolean mayInterruptIfRunning) Attempts to cancel execution of this task. 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. Method Detail
* #### cancel boolean cancel(boolean mayInterruptIfRunning) 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 [isDone()](../../../java/util/concurrent/Future.html#isDone--) will always return `true`. Subsequent calls to [isCancelled()](../../../java/util/concurrent/Future.html#isCancelled--) will always return `true` if this method returned `true`. Parameters: `mayInterruptIfRunning` \- `true` if the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete Returns: `false` if the task could not be cancelled, typically because it has already completed normally;`true` otherwise * #### isCancelled boolean isCancelled() Returns `true` if this task was cancelled before it completed normally. Returns: `true` if this task was cancelled before it completed * #### isDone boolean isDone() 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`. Returns: `true` if this task completed * #### get [V](../../../java/util/concurrent/Future.html "type parameter in Future") get() throws [InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang"), [ExecutionException](../../../java/util/concurrent/ExecutionException.html "class in java.util.concurrent") Waits if necessary for the computation to complete, and then retrieves its result. Returns: the computed result Throws: `[CancellationException](../../../java/util/concurrent/CancellationException.html "class in java.util.concurrent")` \- if the computation was cancelled `[ExecutionException](../../../java/util/concurrent/ExecutionException.html "class in java.util.concurrent")` \- if the computation threw an exception `[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang")` \- if the current thread was interrupted while waiting * #### get [V](../../../java/util/concurrent/Future.html "type parameter in Future") get(long timeout, [TimeUnit](../../../java/util/concurrent/TimeUnit.html "enum in java.util.concurrent") unit) throws [InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang"), [ExecutionException](../../../java/util/concurrent/ExecutionException.html "class in java.util.concurrent"), [TimeoutException](../../../java/util/concurrent/TimeoutException.html "class in java.util.concurrent") Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available. Parameters: `timeout` \- the maximum time to wait `unit` \- the time unit of the timeout argument Returns: the computed result Throws: `[CancellationException](../../../java/util/concurrent/CancellationException.html "class in java.util.concurrent")` \- if the computation was cancelled `[ExecutionException](../../../java/util/concurrent/ExecutionException.html "class in java.util.concurrent")` \- if the computation threw an exception `[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang")` \- if the current thread was interrupted while waiting `[TimeoutException](../../../java/util/concurrent/TimeoutException.html "class in java.util.concurrent")` \- if the wait timed out
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