Which Pattern should i use for a multiplataform application?

I want to develop a podCast client application for Android. Later I plan to port this application to Desktop. I want to build the desktop version in JavaFX, so it would run on PC and MAC.

Since Android also uses Java, I want to create my business classes in a library that could be used by both platform. I imagine that i would have a platform independent central library with my business classes. This library would access a platform specific library for tasks like download a file, play a file etc.

What would be a good design pattern I could use for that? I read about Abstract Factory, but i'm still in doubt as to how would i create the factory class and pass it to the main library, without having to do it in each method I call.