Two possible types for a property

I have a class that is a leaf in the composite pattern. This class has a property that can be either of type A or type B. Their only common interface is of type Object.

How should I support this.

I can

1. have a add method for each type. That would however mean that I should have two properties of type A and B and should check for null when I want to get the right property.

2. have one property of type of Object. That would mean I had to check to see which kind of instance it is when I get the property.

What is the best solution for this typ开发者_运维问答e of problem? Or any better solutions?

Personally I would choose the single Object property approach. Document what types of objects the property may return, and let the calling code use the available language features to determine the object type, and cast as necessary. Implementing two properties is kinda reinventing the "is-a" operator of your language, and will quickly become unmanageable if you ever need to add more possible types.

Well if you are using a language that supports type abstraction (like Generics in Java or Templates in C++) you can just set that property as a generic type. If not, use Object, Having a method for each type is just an ugly hack (and unmaintanable, if you add more types later).