Introduction to OOP Chapter 10: Subclasses and Subtypes: next previous audio real text

Subclasses are not Necessarily Subtypes

It is easy to create a subclass that is not a subtype -- think of NonStack.

It is also possible to create subtypes that are not subclasses. Think of Array in Smalltalk. This class is characterized by the following interface:

	at: input put: value
	at: int
But class Dictionary will also support the same interface, and perform similar actions -- but Dictionary is not a subclass of Array.
Intro OOP, Chapter 10, Slide 06