Should Java 8 getters return optional type?

Question

Optional type introduced in Java 8 is a new thing for many developers.

Is a getter method returning Optional<Foo> type in place of the classic Foo a good practice? Assume that the value can be null.

Answer 1

Of course, people will do what they want. But we did have a clear intention when adding this feature, and it was not to be a general purpose Maybe type, as much as many people would have liked us to do so. Our intention was to provide a limited mechanism for library method return types where there needed to be a clear way to represent "no result", and using null for such was overwhelmingly likely to cause errors.

For example, you probably should never use it for something that returns an array of results, or a list of results; instead return an empty array or list. You should almost never use it as a field of something or a method parameter.

I think routinely using it as a return value for getters would definitely be over-use.

There's nothing wrong with Optional that it should be avoided, it's just not what many people wish it were, and accordingly we were fairly concerned about the risk of zealous over-use.

(Public service announcement: NEVER call Optional.get unless you can prove it will never be null; instead use one of the safe methods like orElse or ifPresent. In retrospect, we should have called get something like getOrElseThrowNoSuchElementException or something that made it far clearer that this was a highly dangerous method that undermined the whole purpose of Optional in the first place. Lesson learned. (UPDATE: Java 10 has Optional.orElseThrow(), which is semantically equivalent to get(), but whose name is more appropriate.))

Answer 2

After doing a bit of research of my own, I've come across a number of things that might suggest when this is appropriate. The most authoritative being the following quote from an Oracle article:

"It is important to note that the intention of the Optional class is not to replace every single null reference. Instead, its purpose is to help design more-comprehensible APIs so that by just reading the signature of a method, you can tell whether you can expect an optional value. This forces you to actively unwrap an Optional to deal with the absence of a value." - Tired of Null Pointer Exceptions? Consider Using Java SE 8's Optional!

I also found this excerpt from Java 8 Optional: How to use it

"Optional is not meant to be used in these contexts, as it won't buy us anything:

• in the domain model layer (not serializable)
• in DTOs (same reason)
• in input parameters of methods
• in constructor parameters"

Which also seems to raise some valid points.

I wasn't able to find any negative connotations or red flags to suggest that Optional should be avoided. I think the general idea is, if it's helpful or improves the usability of your API, use it.