You saw an example of implementing an interface in the previous lesson. You can read more about interfaces here—what they are for, why you might want to write one, and how to write one.
This section describes the way in which you can derive one class from another. That is, how a subclass can inherit fields and methods from a superclass. You will learn that all classes are derived from the Object class, and how to modify the methods that a subclass inherits from superclasses. This section also covers interface-like abstract classes.