Jeff Friesen Figure 2. Hovercraft multiply inherits from land vehicle and water vehicle categories Categories are described by classes. Java supports single inheritance through class extension ...

Java’s interface ... multiple implementation inheritance, and the root of all classes. In addition, I have introduced the specialized topics of enumerated types and singletons.

A method might accept a specific type and its subclasses, but you want to restrict usage to a select few implementations of your own design. Java's open inheritance model can feel like an open ...