Summary

Inheritance solves the problem of related types that share a great deal of common behavior but differ across some dimension. It allows you to isolate shared code and implement common algorithms in an abstract class, while also providing a structure that permits subclasses to contribute specializations.

The best way to create an abstract superclass is by pushing code up from concrete subclasses. Identifying the correct abstraction is easiest if you have access to at least three existing concrete classes. This chapter’s simple example relied on just two but in the real world you are often better served to wait for the additional information that three cases supply.