何时使用 CompletableFuture#thenApply(..) 而不是 thenApplyAsync(..)？

Question

In context of CompletableFuture I understand that thenApply(..) may use the current thread and may use the a pre-defined executor (eg ForkJoinPool) while thenApplyAsync(..) ensures that the pre-defined executor will be always used.

Far as I see the thenApplyAsync(..) seems be more "reliable" as it never blocks the current thread while thenApply(..) might be a surprise.

My question: Which example/scenario would be valid to use thenApply(..) rather than thenApplyAsync(..) ?

Thanks, Christoph

Answer 1

Yes, thenApplyAsync would use some excecutor. This means that some Runnable object must be created and put in the executor's queue. If the function you want to execute after the complethion of this CompletableFuture is very simple, then invoking this method directly may be more efficient than creating envelope Runnable.