Thus, our sixth principle of object-oriented programming is that classes can be organized into singly-rooted tree structure, called an inheritance hierarchy. The benefit of doing this is that information, both data and behavior, that I associate with one level of abstraction in this class hierarchy is automatically applicable to lower levels of the hierarchy.
This will turn out to be both a great organizational aid, as well as a great tool for reducing the amount of code that must be written for new applications.