Is there a convention for maintaining both a free and pro app version from the same codebase in Eclipse?

I am releasing two versions of an app--free and pa开发者_如何学Goid. The differences between the two are few, and I would like to release both using the same codebase (maybe a different constant defined for the other build?). Has anyone done this? Can someone point me in the right direction? Thanks!

Use an Android library project, which was specifically designed for your free/paid scenario.