Decorator

Origin:

GoF 95

Reason:

Extend the functionality of an instance of a class, but not of all instances of the class.

Synopsis:

Define a class, the Decorator, that encloses the object whose functionality is to be extended.

Example:

Consider a security and monitoring system. When the object controlling a door receives a request to open a door, the monitor controlling the door displays the doorway. There are several classes for opening a door and several classes for displaying a doorway.

Solution:

Service	There is both an interface and one or more concrete classes. Objects of these classes provide a service.	Doorway monitor
Wrapper	There is both an interface and one or more concrete classes. Objects of these classes delegate operations to Service.	Door opener