Writting java/android code in android mode

I'm making an Android app in the processing language, and would like to use android classes like editText. Unfortunately the Apwidgets library seems to be unsupported for processing 3.0.1.

So my question is: How do you write standard android code in a processing sketch? Where do I put UI XML? Where in my sketch d0 I put things like eventListeners and eventHandlers? A simple example of how to add an Android element (like a button) and use eventhandler + listener?

Sincerely me