装饰器图案装饰器限制

Question

I am currently writing a program using the decorator pattern. I am trying to find out how to limit the amount of decorators I can add to the first class. Such as:

Pizza plainPizza = new PlainPizza;
Pizza sausage = new Sausage(plainPizza);

How could I code this where I can be limited to the amount of decorators I add on. Such as if I try to add this on top of the previous code:

Pizza pepperoni = new Pepperoni(sausage);

How can I prevent it from allowing pepperoni to be added/wrapped?

I am attempting to use a throw exception, but the problem is, my decorators call its superclass, so I can't test before initializing the instance variable!

Answer 1

You can use a Builder pattern to create a builder that will apply all types of decorators that you need. Builder could also internally keep track of how many decorators you applied and react accordingly if attempt to add more than it's allowed is made.