While very few people in physics use Java for anything serious, it is still a good idea to learn the fundamental concepts behind Java and object-oriented programming. Learning different paradigms of programming will make programming more natural, and OOP is the most widely used paradigm today (though it's rather lacking in the sciences). On the other hand, if you're already proficient in multiple languages, intro java classes might be completely below you, and you'll be extremely bored. You have to really want to learn the concepts, not just the execution, for it to be interesting.
Thanks! Awesome nickname by the way :). I have been learning Fortran 90/95 for about a year and I must say that there is a surprising level of sophistication despite seeming bare-bones. I had more problems with it than with Haskell at the start… which is something that I would never suspect if not for putting effort to both. Mind expanding on that one?You have to really want to learn the concepts, not just the execution, for it to be interesting.