I personally think Singletons are silly. Why not just use package (class) variables? What's the point of being able to instantiate a class when you only want one instance (which you get for free with package variables)? If you must have Singletons, the way you've done it looks fine - it's a simple concept, it should be simple to implement.

But what's this about a database class for every table? That doesn't sound right...