Some more notes on general principles of object-oriented programming (although some were given previously, I'm still getting a lot of requests for basic explanations) are available here (this time from the University of Missouri at Kansas City).
We've covered such things as dynamic binding, the use of Java's
instanceof, and assigning from more specific types to
more general and vice versa.
Here is an article which covers all this.
A complete set of course notes (from Queen's University, Belfast), with examples and exercises, which covers much of the more advanced aspects of Java programming covered in our second semester is available here. Click on the "Full Notes" link from this page, though the other links here lead to some interesting stuff as well.
Matthew Huntbach 2nd February 2001