decorator

Decorator

Decorator Pattern adds behavior or state to an object at run-time.

Code

Print is an interface implemented by Photo and DecoratedPrint. Photo is simply an implementation of Photo. DecoratedPrint is an abstract class that is expected to be overriden by different kinds of print decorators such as FramedPrint and LaminatedPrint. DecoratedPrint has reference to the wrappee (a Print that it is decorating on) so its concreate classes - FramedPrint and LaminatedPrint - can only focus on decorating the wrappee and pay no attention to how wrappee is owned.

Note

Many online examples name the decorator class with SomethingDecorator directly, which seems to violate Liskov Substitution Principle (LSP) to me. A subclass should be able to replace its parent class; however, it's hard to say a SomethingDecorator is a Soemthing. For example, topping isn't a pizza. Instead, I think it's better to name it as XXXDecoratedSomething e.g. DecoratedPrint in my example code.

Reference

• http://www.vincehuston.org/dp/decorator.html (Really good.)
• https://www.tutorialspoint.com/design_pattern/decorator_pattern.htm
• https://stackoverflow.com/questions/12854778/abstract-class-vs-interface-in-c