I learned one of the most important OOD techniques 10 years ago on an OOD workshop. It has since become known as the Dependency Inversion Principle.

I was recently challenged about one of our corporate programming guidelines - "Separate the logic from the interface where possible." On the face of it, it seems such a common-sense rule to me, that I actually struggled to explain why it is a rule.

What is a servlet and why use one?