Interface Design

Right, this is my last thread for today, all I have done is post shite.

I am feeling as if it is time I actually learn to do proper interface design, I have had a good look over LibGDX and how it is basically fully designed with interfaces. I sort of get how it works but at the same time it confuses the hell out of me.

Hit me with your best Interface Design articles, tutorials, books whatever.

I want to learn this sorcery! I shall Extend no more, I must implement!