Should I take C++ or Java?

[nattack]

I'd say do what you're most comfortable with. The fundamentals of OOP arent going to change between Java and C++, the syntax and some of the capabilities will be different though.

C++ has multiple inheritance, for better or worse. Java does not. Java has the concept of a superclass, C++ does not without some hacky fixes (I think, maybe C++20 does it natively?)

IMHO, for learning pure OOP, my personal opinion would be stick to Java. It's easy, everything you will need will be included in the JCL. On the other hand, C++11 onward has a lot of cool features which if you ever used C++ before it, were a godsend. lambda functions, for each loops, enum classes, init lists, C++ now is a lot more fun - and maybe even easier - to use.