An extended class adds function to a defined class. An extended class consists of one or more methods (which define the added function or behavior). These methods are contained in applications other than the application that contains the defined class.

Extended classes enable you to add methods to defined classes existing in the system, without changing the behavior of those existing classes. The methods change the behavior of only the applications to which you are adding the methods.

When you create an extended class, you do not add a new class to the system. You merely add methods to a defined class.

As with defined classes, each extended class can be contained in only one application within one image.