Future

get

cancel

Future

Future<?>

null

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 methodwhen the computation has completed, blocking if necessary until it is ready. Cancellation is performed by themethod. 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 afor the sake of cancellability but not provide a usable result, you can declare types of the formand returnas 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(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; } } }

Future

Runnable

Executor

submit

FutureTask<String> future = new FutureTask<String>(new Callable<String>() { public String call() { return searcher.search(target); }}); executor.execute(future);

The FutureTask class is an implementation ofthat implements, and so may be executed by an. For example, the above construction withcould be replaced by: