Is there a default ExecutorService or am I doomed to create one and maintain it to get Future objetcs?

Question

The only way to get a Future, from what I understand, is to use an ExecutorService, which is obtained for instance via Executors.newFixedThreadPool(10) (btw, how do you how many threads to use? is there some thumb rule?).

So what I don't understand, is whether am I supposed to use:

ExecutorService executorService = Executors.newFixedThreadPool(n);

And then save it (e.g. in some top level IoC) and call the executorService whenever I need new Future?

Isn't there like a default Java's built-in ExecutorService I can used, thus avoiding the nag of ExecutorService initialization and maintenance?

Answer 1

default Java's built-in ExecutorService

ForkJoinPool.commonPool() - Returns the common pool instance. This pool is statically constructed; its run state is unaffected by attempts to shutdown() or shutdownNow(). However this pool and any ongoing processing are automatically terminated upon program System.exit(int)...

Future<?> future = ForkJoinPool.commonPool().submit(() -> { /* something to do */}) ;

But there is a more modern way: CompletableFuture

CompletableFuture<Void> future = CompletableFuture.runAsync(() -> { /* something to do */});

Answer 2

Isn't there like a default Java's built-in ExecutorService I can use...?

There is in Java8.

Read the Javadoc for java.util.concurrent.CompletableFuture.supplyAsync(...).