You can't, unless it's in a standard library or a core dependency used by millions of people.

That's one of the reasons why functional code is generally easier to read. A lambda defined a few lines above whatever you're reading gives you the implementation details right there while still abstracting away duplicate code. It's the best of both worlds. People who's idea of "functional programming" is to import 30 external functions into a file and compose them into an abstract algorithm somewhere other than where they're defined write code that's just as shitty and unreadable as most Java code.