No, don't do Java.
I don't know HOW you decided you want to be an Ethical Hacker if you don't know what that entails, but maybe that was a couple of Hollywood movies having their effect on you? (Swordfish?
) , but anyway, to be one, you have to know the lowest levels of things, the very numbers that your chip is crunching. If you already have programmed, you know that your mind can "work that way", the next thing you should learn is Assembly Language. It's NOT easy, but still a heck of a lot easier these days since you can't crash a modern machine running in protected mode than when *I* was learning, MANY MANY years ago
When you have a reasonable handle on it, AND C, try this book: Programming Linux Hacker Tools Uncovered by Ivan Sklyarov (this should take you a couple of years).
Don't let others intimidate you (people older than you). FWIW, *I* am currently learning CSS, which I bloody HATE, so you know more about it than I do!
Tell us how it goes