Because what they are actually like is java.awt — they are the classes used to implement graphics in Smalltalk-80, not some made-up example.
(The "Java in a Nutshell 8th ed, I found has no page numbers. There's a "Subclasses and Inheritance" section which shows how to code PlaneCircle as a subclass of Circle class.
afaict That's a couple of made-up classes that exist solely to show things that can be done with Java classes. Not an example of "compile-time hierarchy of encapsulation that matches the domain model". Later the authors use class A and class B for their examples.)
Because what they are actually like is java.awt — they are the classes used to implement graphics in Smalltalk-80, not some made-up example.
(The "Java in a Nutshell 8th ed, I found has no page numbers. There's a "Subclasses and Inheritance" section which shows how to code PlaneCircle as a subclass of Circle class.
afaict That's a couple of made-up classes that exist solely to show things that can be done with Java classes. Not an example of "compile-time hierarchy of encapsulation that matches the domain model". Later the authors use class A and class B for their examples.)