Is there an equivalent of lambda calculus for object oriented languages?
So what is the equivalent for object oriented languages?


Lambda calculus.

I mean, there is Cardelli's object calculus (and a handful of derivatives), but in general, there's nothing fancy about object oriented languages that requires a new approach to computation. 

It's well known (see TaPL for example) how to extend/encode Records and Mutation (and sub-typing/dispatch) onto/in lambda calculus. The underlying structures don't need to change, even though there are often layers above it that add semantic restriction and make things more usable (member access, implied this, object layouts, etc).