How to represent a multilevel hierarchy in Java

Question

I am trying to make an Android application where you can buy and sell items. I've run into a wall: I am stuck at how to represent categories and sub-categories. Any category can have some number of sub-categories, and these sub-categories can also have sub categories with fields in them, etc.

For instance, let's say you want to sell a pair of your watches, the category and sub categories might be:

-Jewelry
--Men
---Watches
----Rolex

or it might even be

-Jewelry
--Men
---Watches
----Rolex
-----Models
------SubMarine

How would you represent this with a class hierarchy? I can't seem to find a solution that doesn't end out with a ton of classes and something that is difficult to update.

I was thinking of using Jackson/Gson, Mysql/MSSQL for storage and most likely rest services for saving it; bonus points for an answer that can integrate with those technologies.

Answer 1

Inheritance would be a naive approach. A sub-class per Category and Subcategory cannot scale.

What about sub-sub-categories? Oh, my.

Maybe a better approach is to stick with a Category class and make it a Composite , or just create a tree of Category instances. That way you can assemble trees of categories to your heart's content by adding instances and data rather than new classes.