Oh I see someone has already mentioned the Hour of Code website! Right on. Instead I will add that on their "Go Beyond an Hour" tab they have a window featuring links to colleges that offer online courses to a wide variety of programming languages - Java is just one of many. Yes it costs money, but at least you know you will be learning the right stuff from people that actually know their stuff.

People aren't going to teach you Java for free, buy a good book to learn Java or reverse engineer Java programs, mods. The problem with a book is that you don't learn to code with Minecraft as a reference library. If you just want a fun experience and learn the very basics, you can check out this application that Code.org made.

Lol, good laughs.
No-one will teach you for free.

Besides, I see you are a keen learner, so my suggestion is to learn Lua, C#, C++, make your own game (code your own physics, lighting engine etc if you are sure about yourself, or use ready-made like Unity or Source, and earn money, but you can learn whatever language you want.

By the way, imagine yourself a professional, vastly experienced software engineer and some snobby kid (not you) comes up to you and asks you to teach him how to code for free.

Hmmmm.... No.

The only free way to learn something is to reverse engineer and find some half-azzed tutorials on YouTube to help you out.

Teaching Java takes A LOT of time and I doubt anyone would be willing to do it for free, any experienced person that is.