Attaches additional responsibilities to an object dynamically. Decorators provide a
flexible alternative to subclassing for extending functionality.
Category:
Structural
UML Diagram:
Description of the Demonstration:
A parent class, Beverage, has four main sub-classes, DarkRoast,
HouseBlend,Espresso, and Decaf. These represent the four types
of beveages available from the Starbuzz Coffee Shop. Another
sub-class, CondimentDecorator, serves as the parent class for
all condiments to be added to the beverages following the Decorator
Design Pattern. In the demonstration three "customers" place orders,
giving first the Beverage type they want, e.g. "I'll have a DarkRoast"
then the condiments they want, e.g. "with milk and mocha". The
Beverage is then successively decorated with each of the condiments,
e.g. the instance of Milk is given a pointer to an instance of
DarkRoast, then an instance of Mocha is given a pointer to
the instance of Milk. A call can then be made to getCost on the
Mocha which calls getCost on Milk which call getCost on Darkroast.
The final result gives the total cost of this Beverage. A similar
chain of calls is used to print the description of the Beverage.
Code:
Click here to download a
zip file containing all the source files and an executable of the
Demonstration. See the _ReadMe.txt file in the zip.
