Refactoring: Improving the Design of Existing Code

by Martin Fowler

Computer Science is the discipline that believes all problems can be solved with one more layer of indirection. —Dennis DeBruler

The lesson is: Even if you know exactly what is going on in your system, measure performance, don't speculate. You'll learn something, and nine times out of ten, it won't be that you were right!

The secret to fast software, in all but hard real-time contexts, is to write tunable software first and then to tune it for sufficient speed.

I gain nothing from using isNull rather than == null. The gain comes as I move behavior to the null customer and remove conditionals.