Question

Say I am writing a user interface for a hardware accessory. There are two versions of the accessory – let’s say Widget Lite and Widget Pro.

Widget Pro can do everything that Widget Lite can do, but with a few more options and can do a few things that Widget Lite can’t. In more detail, Widget Lite has one channel, widget Pro has two, so when it comes to something analogous to volume control, I need only one control for the Lite, but two for the Pro allowing independent control.

In my first attempt at building an application to handle this, I had the class representing Widget Pro extend Widget Lite, but then I’ve ended up with all sorts of conditional cases to handle the differences which seems ugly. Does anyone know a suitable design pattern to help with such a situation? My imagination is drawing a blank in coming up with synonymous situations that might help in my search.

Answer 1

I would do it as follows:

              AbstractWidget (Abstract class)
                   /\
                  /  \
                 /    \
                /      \
               /        \
         WidgetLite   WidgetPro

The common code would go into the AbstractWidget (abstract because, it shouldn’t be instantiated) and the behaviour that is different between these two classes would go into the concrete classes.