compact1, compact2, compact3
java.util.concurrent
Interface Future<V>
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- Type Parameters:
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V- The result type returned by this Future'sgetmethod
- All Known Subinterfaces:
- Response<T>, RunnableFuture<V>, RunnableScheduledFuture<V>, ScheduledFuture<V>
- All Known Implementing Classes:
- CompletableFuture, CountedCompleter, ForkJoinTask, FutureTask, RecursiveAction, RecursiveTask, SwingWorker
public interface Future<V>AFuturerepresents 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 methodgetwhen the computation has completed, blocking if necessary until it is ready. Cancellation is performed by thecancelmethod. 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 aFuturefor the sake of cancellability but not provide a usable result, you can declare types of the formFuture<?>and returnnullas a result of the underlying task.Sample Usage (Note that the following classes are all made-up.)
Theinterface ArchiveSearcher { String search(String target); } class App { ExecutorService executor = ... ArchiveSearcher searcher = ... void showSearch(final String target) throws InterruptedException { Future<String> future = executor.submit(new Callable<String>() { public String call() { return searcher.search(target); }}); displayOtherThings(); // do other things while searching try { displayText(future.get()); // use future } catch (ExecutionException ex) { cleanup(); return; } } }FutureTaskclass is an implementation ofFuturethat implementsRunnable, and so may be executed by anExecutor. For example, the above construction withsubmitcould be replaced by:FutureTask<String> future = new FutureTask<String>(new Callable<String>() { public String call() { return searcher.search(target); }}); 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:
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FutureTask,Executor
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method and Description booleancancel(boolean mayInterruptIfRunning)Attempts to cancel execution of this task.Vget()Waits if necessary for the computation to complete, and then retrieves its result.Vget(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.booleanisCancelled()Returnstrueif this task was cancelled before it completed normally.booleanisDone()Returnstrueif this task completed.
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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 whencancelis called, this task should never run. If the task has already started, then themayInterruptIfRunningparameter 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()will always returntrue. Subsequent calls toisCancelled()will always returntrueif this method returnedtrue.- Parameters:
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mayInterruptIfRunning-trueif the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete - Returns:
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falseif the task could not be cancelled, typically because it has already completed normally;trueotherwise
isCancelled
boolean isCancelled()
Returnstrueif this task was cancelled before it completed normally.- Returns:
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trueif this task was cancelled before it completed
isDone
boolean isDone()
Returnstrueif this task completed. Completion may be due to normal termination, an exception, or cancellation -- in all of these cases, this method will returntrue.- Returns:
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trueif this task completed
get
V get() throws InterruptedException, ExecutionException
Waits if necessary for the computation to complete, and then retrieves its result.- Returns:
- the computed result
- Throws:
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CancellationException- if the computation was cancelled -
ExecutionException- if the computation threw an exception -
InterruptedException- if the current thread was interrupted while waiting
get
V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.- Parameters:
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timeout- the maximum time to wait -
unit- the time unit of the timeout argument - Returns:
- the computed result
- Throws:
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CancellationException- if the computation was cancelled -
ExecutionException- if the computation threw an exception -
InterruptedException- if the current thread was interrupted while waiting -
TimeoutException- if the wait timed out
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Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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