In Chapter 7, “Classes,” you learned how to write class files and how classes help you organize code into external files. The chapter also demonstrated how you can organize class files into related packages. This chapter aims to show you how to write more advanced classes that extend the functionality of an existing class. This is a useful subject, because you might find yourself extending your own custom classes or existing classes so that you can add new methods and properties.
For more information on inheritance, see the following topics: