6. Extending classes

This chapter covers Subclassing Extending classes Creating custom objects Class clusters Categories Existing class modification

Classes, which consist of instance variables and methods, can be extended by being modified, expanded, or abstracted. Class extension is one of the fundamental ideas of object-oriented programming. The ability to extend a class promotes code reuse and compartmentalization, and it’s the sign of a well-thought-out project. We investigate the subtleties of the various approaches to extending classes.