Comments on: Simplifying inheritance hierarchies using powertypes and Java 5 enums

By: danhaywood

danhaywood — Thu, 08 Apr 2010 20:28:27 +0000

Hi Mohamed,

When you say one more type, I guess you mean one more instance of the enum (eg StockType#DVD). In that case, though, I don’t think this is the technique for you. The point of an enum, of course, is that all known values are enumerated. If you wanted to support additional instances, then you’d need to open up the code somehow. In DDD terms, it’d probably become an entity.

On the other hand, perhaps you aren’t interested in adding new instances, but want somehow to change the behaviour associated with the instance. In which case, check out the next post in the series.

Cheers
Dan

By: Mohamed El-Beltagy

Mohamed El-Beltagy — Wed, 24 Mar 2010 13:28:59 +0000

First of all, I am very sorry for commenting although I know nothing about NakedObjects. But my question is not related to NakedObjects, I think.
My question is: What if I would like to add one more type to the StockType enum?
I know that means that I have to add it in the enum declaration. But what if I don’t have access to that enum’s source code?
For example, what if I’m using an already made product and want to extend it to do little customization?

By: Casper Bang

Casper Bang — Wed, 24 Mar 2010 11:44:40 +0000

Thanks for pointing out this technique. I had forgotten about it since reading about it in Effective Java.