
56 9 Chapter 3: Frameworks and Object-Oriented Programming
sion is a minor point because the context is almost always
clear.
Object-Oriented Design Issues
You define an object with a class definition that specifies its
variables and methods. You create a specific instantiation of
that object to contain a single set of data.
In a nutshell, that's it. However, there are a few design issues
that are important in all object-oriented programming lan-
guages and that are particularly relevant to Cocoa and Mac
OS X.
Inheritance
Polymorphism
An object may be based on another object--may in fact "de-
scend" from that other object.