Can a class have only one instance?
Yes. Again, there is no problem as far as the formalism goes. An empty table or a table that always contains only one instance is perfectly fine. If there is always one instance, you have to ask why. Many times it is because the functions at the focus of your interest only apply to one instance. But, as you extend your scope, it becomes apparent that more than one instance is possible. If we are building a control system for an inspection station, we may know there is only ever one station. But the minute we extend this system to networked control of many stations, more instances are entered into the table. It is also possible that you have a useless class that really shouldn’t be a class.
