Completing CompletableFuture<T> before adding a callback

Question

Is there any chance that by the moment thenApply / thenAccept methods are called for new CompletableFuture object, the future's execution will have already been finished and setting handlers via aforementioned methods won't have any effect? I am not just having these two methods in mind, but the whole bunch of ~50 methods that accept handlers of the CompletableFuture API.

CompletableFuture<String> f = CompletableFuture.supplyAsync(() -> toString());

f.thenApply(s -> f); // will be called if "f" completes before this line is invoked?

Answer 1

Yes.

If a promise has already resolved, any callbacks you add in the future will execute immediately.