Java Language Executor, ExecutorService and Thread pools Retrieving value from computation - Callable
Example
If your computation produces some return value which later is required, a simple Runnable task isn't sufficient. For such cases you can use ExecutorService.submit(Callable<T>) which returns a value after execution completes.
The Service will return a Future which you can use to retrieve the result of the task execution.
// Submit a callable for execution
ExecutorService pool = anExecutorService;
Future<Integer> future = pool.submit(new Callable<Integer>() {
@Override public Integer call() {
//do some computation
return new Random().nextInt();
}
});
// ... perform other tasks while future is executed in a different thread
When you need to get the result of the future, call future.get()
-
Wait indefinitely for future to finish with a result.
try { // Blocks current thread until future is completed Integer result = future.get(); catch (InterruptedException || ExecutionException e) { // handle appropriately } -
Wait for future to finish, but no longer than specified time.
try { // Blocks current thread for a maximum of 500 milliseconds. // If the future finishes before that, result is returned, // otherwise TimeoutException is thrown. Integer result = future.get(500, TimeUnit.MILLISECONDS); catch (InterruptedException || ExecutionException || TimeoutException e) { // handle appropriately }
If the result of a scheduled or running task is no longer required, you can call Future.cancel(boolean) to cancel it.
- Calling
cancel(false)will just remove the task from the queue of tasks to be run. - Calling
cancel(true)will also interrupt the task if it is currently running.
