Polymorphic substitution in Java

I'm seeking a simple/short explanation of what polymorphic substitution is in java (using object orientated systems) -- something NOT aimed at an expert.

All the resources I find on the net are OTT :confused: and don't explain it clearly enough, i.e. using examples in straightforward language.

(I have found an okay explanation on the British Computer Society website but i'd still like a better one if anyone has any decent links....) :)

Chapter 7 of Thinking in Java, Third Edition (it's a free online book that you can buy if you want to... see http://www.mindview.net ) covers polymorphism in detail.

The basic idea of it is using late binding (binding method calls to method bodies at runtime rather than compile-time) to allow you to call a method of a class without knowing specifically which class it is but rather only knowing which class the specific classes are derived from.

Exactly what I was looking for, thanks cfc :D