I wish people would be less opinionated about things like this. I've completed exercises for books or courses in C, C++, Lisp, Scheme, Go, Python, Javascript, Ruby, Rust, Java, Scala, Clojure, Prolog, Assembly, etc. It's not a big deal. Nobody is telling anybody they have to then program in that language for the rest of their lives. Be open to new experiences. Java really isn't difficult or alien or bad enough to complain that it's the wrong language and expecting book x to be in your preferred language z when there are dozens one could choose is so...closed-minded.
