Chapter    4

Discovering Inheritance, Polymorphism, and Interfaces

An object-based language is a language that encapsulates state and behaviors in objects. Java’s support for encapsulation (discussed in Chapter 3) qualifies it as an object-based language. However, Java is also an object-oriented language because it supports inheritance and polymorphism (as well as encapsulation). (Object-oriented languages are a subset of object-based languages.) In Chapter 4 I introduce you to Java’s language features that support inheritance and polymorphism. Also, I introduce you to interfaces, Java’s ultimate abstract type mechanism.

Building Class Hierarchies

We tend to categorize stuff by saying things like “cars are vehicles” or “savings accounts are ...

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