Class hierarchy is also called an inheritance hierarchy. It shows a complete hierarchy of classes and subclasses that are derived from their parent classes. For example, university community can be divided in to employees, students, and alumni. Employees are again divided in to staff and faculty members. Students are divided in to undergraduate and graduate students. Below is the class hierarchy diagram for university community.
Deriving a subclass
The derived new class is called a subclass. It inherits the attributes and methods of its base class. It can also have its own attributes and methods in addition to the ones that are inherited from the parent class. The keyword �extends� is used to derive a subclass in JAVA.