Josh Bloch says this (see his must-read book Effective Java for more details) :
"The constant interface pattern is a poor use of interfaces. That a class uses some constants internally is an implementation detail. Implementing a constant interface causes this implementation detail to leak into the class’s exported API. It is of no consequence to the users of a class that the class implements a constant interface. In fact, it may even confuse them. Worse, it represents a commitment: if in a future release the class is modified so that it no longer needs to use the con-stants, it still must implement the interface to ensure binary compatibility. If a nonfinal class implements a constant interface, all of its subclasses will have their namespaces polluted by the constants in the interface."
he then goes on to suggest using a non-instantiable class instead. e.g :
I totally agree, on top the reasons above this way is much neater and makes more sense; how many times does the is-a (or behaves-as-a) test hold up when constant interfaces are used ? I've never seen it.
[ November 13, 2002: Message edited by: Tom Hughes ]