How to learn more...

Hello everyone,

Recently I began to learn Java by using online tutorials. I am coming into Java from Lua. The main issue is grasping the OOP part (since Lua isn't a OOP language.). I was wondering if anyone could recommend a book to help me learn more Java (I know some, but not enough to do much.), and/or show me some good online tutorials.

Like I said the main thing I'm having trouble fully understanding is the classes and keywords (like extends, interface, implements, package, etc.). If anyone can help me with that, that would be great. Thanks!