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The Role of Inheritance

The next pillar of OOP, inheritance, boils down to the language’s ability to allow you to build new

class definitions based on existing class definitions. In essence, inheritance allows you to extend the

behavior of a base (or parent) class by inheriting core functionality into the derived subclass (also

called a 

child class). Figure 5-8 shows a simple example.

You can read the diagram in Figure 5-8 as “A Hexagon is-a Shape that is-an Object.” When you

have classes related by this form of inheritance, you establish “is-a” relationships between types.

The “is-a” relationship is termed classical inheritance.

Here, you can assume that Shape defines some number of members that are common to all

descendents. Given that the Hexagon class extends Shape, it inherits the core functionality defined by

Shape and Object, as well as defines additional hexagon-related details of its own (whatever those

may be).