The only Java program of any consequence I wrote was a multiagent autonomous robot simulator (sounds more complicated than it actually was :-) for an experiment in independent agents. It was fun, but after I was done, there was absolutely no motivation left to continue and I soon got into Python instead.

Java is simply not a "fun" language! If you're a student and looking for a job, knowing the language basics is enough, no one hiring out of school will expect you to be an expert. Much more important to know the OO principles it's supposedly based on.