I am stuck

I do not understand one of the nitpicks I got.
The basic logic behind my program is to except a serial number as a command line argument then retrieve the description from the HashMap using the serial number. After retrieving the description I use an if/else construct to instantiated the desired object based on the passed in serial number. I use the follow basic setup for object creation:
where each Child class extends AbstractParentClass and overrides an AbstractParentClass's method.
Is the if/else stuff wrong? Am I not doing
polymorphism? The object created is not known until runtime and I have followed the examples in the books, so I was under the impression I was doing polymorphism. I looked at putting the different objects in an array, but didn't see the point in it. Or am I just missing the point of the remark (nitpick) all together.
I can already hear myself saying "duh!" and leaving a red mark on my forehead
[This message has been edited by Richard Boren (edited June 28, 2001).]