[hepta]

I assumed the omission was for brevity, but there are annotations and 'final' in a lot of places.

Similarly, methods for mutation (compulsory, no less!) are red flag in FP.

[john_reel]

As someone who isn’t familiar with functional programming at all or too familiar with Java, where do I start?

[ptero]

Unless you have a strong reason to use Java, I'd stay far out of it in learning FP. Pick a language where FP model fits well into the language core (e.g., ocaml, Haskell; google for other options), not glommed on as an afterthought to a general purpose language.

[hepta]

Depends on your goals, Java isn't the best if your aim is to learn FP.

[odabaxok]

How about https://www.coursera.org/learn/progfun1 ?