This example also shows a misbehaving toString() implementation in the subclass. If we extend the Fraction class and mark the methods we don’t want overridden with final, there could be ...

What you’ll learn in this Java tutorial. The first half of this introduction to Java inheritance teaches you how to use the extends keyword to derive a child class from a parent ... Final classes.

Marking a class as final prevents all inheritance, by anyone -- even the original developer cannot inherit from one of their own final classes. It's a powerful but potentially messy design constraint.