UDK uses C++ or unreal script.
Unity uses C#, javascript (no relation to java at all) or Boo.

Learning java and then something else is perfectly fine.

How much of the game you will be programming yourself varies on the engine. CryEngine is heavily involved, UDK not so much but still heavily involved. Unity you still have to write code but not as much. If you were to write your own engine then it will probably be purely code work with the exception of drawing textures and making 3d models in the editors of your choice.

EDIT, corrected a few mistakes

UDK uses C++ or unity script.

I think you meant Unreal Script.

Unity uses C#, javascript (no relation to java at all) or Boo. I think it might also do C++

Unity doesn't support C++. The rest are true, though. People usually say "UnityScript" instead of JavaScript when referring to Unity's JavaScript, since they're pretty much unrelated asides from tiny syntax similarities.

I think you meant Unreal Script.

Sorry, wasn't thinking straight.
Corrected original post.

I personally think if you are new to programming, start with python. Very simple and you can get some basics... Java is also really good to start with. Save C++ for later. It's better to get basics down first.

Well his school course is going to be teaching java anyway.

[quote name='6677' timestamp='1339882514' post='4949903']
UDK uses C++ or unity script.

I think you meant Unreal Script.

Unity uses C#, javascript (no relation to java at all) or Boo. I think it might also do C++

Unity doesn't support C++. The rest are true, though. People usually say "UnityScript" instead of JavaScript when referring to Unity's JavaScript, since they're pretty much unrelated asides from tiny syntax similarities.
[/quote]

Unity pro has C++ plugin support though (primarily useful to access other middleware), and if you buy a sourcecode license you can use C++ to modify the engine.