I had a job doing c# development in campus when I was in college, but now I'm working for a software company doing a lot of java, so that's why I would like to

I had a job doing c# development in campus when I was in college, but now I'm working for a software company doing a lot of java, so that's why I would like to broaden my understanding of the language, JVM, performance, etc. I should also note that I have done a lot of ruby development, so I'm not a one trick pony or anything, but working for a company that primarily uses java I would like to have a deep understanding of it.