Java, C#, and C++ all follow a similar OOP strategy. It is based on function calls that are bound at compile time. Depending ont he call, either the direct function call or an offset into a vtable is fixed when compilation happens. By contrast Smalltalk's OOP is based on message passing. Conceptually every method call is a message to the receiving object asking whether it has a method called "Foo."
Smalltalk has no concept of interfaces. It only has similar looking methods. In the C++ group of languages, everything is bound to interfaces. One cannot implement AddRef and Release without also implementing QueryInterface (even if it is just a stub) because they are all part of the IUnknown interface. In Smalltalk, there is no IUnknown. There is only a collection of 3 functions, any of which could be implemented or not.
