Question

I’m developing an application in JAVA SE, with a database in SQL Server.

In this application, I will have three kinds of images:

• First Aid Symbols
• Danger Symbols
• EPIs Symbols

All the images have the following attributes:

• imageID - int
• imageDescription - String
• image - ImageIcon

Thus, the Fist Aid and the EPIs images need this attribute:

• isUsedInRiskAssessment - boolean

My question: what is the best approach to implement this structure?

Inheritance: (image in the link)

http://img194.imageshack.us/img194/6871/inheritance.png

I know inheritance is many times called ‘evil’, but seems like a valid option in this case, except for having a subclass without any other attributes.

Separated Classes:
http://img580.imageshack.us/img580/511/separated.png

Or other?

In my business layer, I want to be able to return all the images (no matter wich type), to the GUI.
I also tought of having a class Image and another class called ImageType. But in this scenario, the Image, when the ImageType is Danger Symbols, would have a non used attribute – the isUsedInRiskAssessment.

This also affects the way I’m going to create the tables in the database.

Hope I’ve explained myself clear. Thanks.

Answer 1

Inheritance is not bad here. But sometimes it would be necessary to write code which would determine the actual type and to do casting, – you won’t like the code you’ll get.
That is why I’d suggest having sometimes unused Boolean property. Actually, three values: true, false and null are what you need. But make sure you mention meaning of null value in your documentation.