There are a couple root-level types of objects you should know : NSOb j ect and id.
Most objects you encounter in iPhone programming inherit from the same root superclass: NSObject. NSObject is one of the core classes provided by the Foundation framework, and among other things it provides the basics of memory management. Memory management is covered in detail in the next chapter, but for now, you should know that NSObject will be the root node of your class hierarchy most of the time.
Foundation is a Cocoa Touch framework that defines the building blocks for your Objective-C classes. The framework includes the ...