CSC 313 – Advanced Programming Topics

Decorator Pattern Intent

Pizza Decorator Pattern Visual

Decorator Pattern Creation Beverage joe = new HouseBlend(); joe = new Mocha(joe); joe = new Whip(joe); joe = new Tall(joe); int mortgage = joe.cost();

Decorators’ Dirty Secrets  Decorators are subclasses of main class

Decorators’ Dirty Secrets  Decorators are subclasses of main class

Decorators’ Dirty Secrets  Decorators are subclasses of main class  Almost recursive

Meet the Decorator Classes

Decorator Pattern Usage Drink martini = new Gin(); martini = new Vermouth(martini); martini = new Ice(martini); martini = martini.shake();

Decorator Pattern Usage Drink martini = new Gin(); martini = new Vermouth(martini); martini = new Ice(martini); martini = martini.shake(); = martini.pour();

Decorator Pattern Usage Beverage joe = new HouseBlend(); joe

Decorator Pattern Usage Beverage joe = new HouseBlend(); joe = new Mocha(joe); joe bev

Decorator Pattern Usage Beverage joe = new HouseBlend(); joe = new Mocha(joe); joe bev

Decorator Pattern Usage Beverage joe = new HouseBlend(); joe = new Mocha(joe); joe = new Whip(joe); joe bev

Decorator Pattern Usage Beverage joe = new HouseBlend(); joe = new Mocha(joe); joe = new Whip(joe); joe = new Mocha(joe); joe bev

Decorator Pattern Usage Beverage joe = new HouseBlend(); joe = new Mocha(joe); joe = new Whip(joe); joe = new Mocha(joe); int mortgage = joe.cost(); joe bev

Decorator Example

Decorators: Good or Bad Pros:  Invisibly add to classes  Enable code reuse  Limit code written  Creates classes that are closed to modification Cons:  No reality in hierarchy  Use mangled recursion  Slow, polymorphic calls used everywhere

For Next Lecture  Lab #3 available on Angel  Asks you to implement Decorator Pattern but  Have time Friday, but may want help profiling  Two (short) readings available on web  Is this method hot or uglier than ____ Mom?  What rules of thumb exist for where to optimize?  How to express improvement so it is meaningful?  Could we compute maximum benefit from opts?