Enthuware

Why is collect(Collectors.averagingDouble(...)) returning a Double and not an OptionalDouble, just like the DoubleStream.average() method?
collect(Collectors.maxBy(...)) results in an Optional<T> just like Stream.max(), so why this difference?

Because Collectors.averagingDouble(...) takes in a ToDoubleFunction, which returns a double instead of OptionalDouble or Optional<T> (as is the case with maxBy).

Okay thanks, and what if the stream is empty? Will it return 0? Or throw an Exception?

What happened when you tried it out?
BTW, the Collectors javadoc, clearly says, "If no elements are present, the result is 0.".

I was planning to try it out, and I read a lot of API, but I missed that. It takes a lot of time to study all the thousand details that are not in de books, but Enthuware exam kits are very helpful. Thanks!