how to best deal with a bunch of references in a class
<p>I have a class that references a bunch of other classes.  I want to be able to add these references incrementally (i.e. not all at the same time on the constructor), and I want to disallow the ability to delete the object underlying these references from my class, also I want to test for NULL-ness on these references so I know a particular reference has not been added.  What is a good design to accomplish these requirements?</p>
