When you write your first object-oriented program, you do not have to begin your real-world modeling from scratch. Rexx provides predefined classes and methods. From there you can create additional classes of your own, according to your needs.
Rexx classes are hierarchical. The original class is called a base class or a superclass. The derived class is called a subclass. Subclasses inherit methods and data from one or more superclasses. A subclass can introduce new methods and data, and can override methods from the superclass.
You can add a class to an existing superclass. For example, you might add the Icon class to the Screen-Object superclass:
In this way, the subclass inherits additional methods from the superclass. A class can have more than one superclass, for example, subclass Bitmap might have the superclasses Screen-Object and Art-Object. Acquiring methods and variables from more than one superclass is known as multiple inheritance:
