The Null Object Pattern

Bobby Woolf
Knowledge Systems Corp.
4001 Weston Pkwy
Cary, NC 27513-2303
919-677-1119 x541
bwoolf@ksccary.com

This submission is not a pattern language, but rather a standalone
pattern. It is written at the level and style of the patterns in
Design Patterns: Elements of Reusable Object-Oriented Software.

Null Object describes a special class with a customized interface
whose implementation is to provide null behavior. It is designed to be
used as part of a hierarchy of classes, all of which have the same
interface. Thus the client does not have to specially test for nil;
the nil behavior is encapsulated inside the null object.