The Class Hierarchy
In Java, all classes are organized into a taxonomy known as the class hierarchy, Class Object is at the top of the hierarchy.
If class s is below class c in the class hierarchy, class s is called a subclass of c, a c is a superclass of s.
The Java class definition
class class-name
{ . . . }
implicitly defines class-name to be a subclass of class Object.
Example. Classes Account, Room, Person, and Matrix are each subclasses of class Object