Head First Design Patterns

Chapter 3. The Decorator Pattern: Decorating Objects

Just call this chapter “Design Eye for the Inheritance Guy.” We’ll re-examine the typical overuse of inheritance and you’ll learn how to decorate your classes at runtime using a form of object composition. Why? Once you know the techniques of decorating, you’ll be able to give your (or someone else’s) objects new responsibilities without making any code changes to the underlying classes.

Welcome to Starbuzz Coffee

Starbuzz Coffee has made a name for itself as the fastest growing coffee shop around. If you’ve seen one on your local corner, look across the street; you’ll see another one.

Because they’ve grown so quickly, they’re scrambling to update their ordering systems to match their beverage offerings.

When they first went into business they designed their classes like this...

In addition to your coffee, you can also ask for several condiments like steamed milk, soy, and mocha (otherwise known as chocolate), and have it all topped off with whipped milk. Starbuzz charges a bit for each of these, so they really need to get them built into their order system.

Here’s their first attempt...

Brain Power

It’s pretty obvious that Starbuzz has created ...