Java: Inherit and Be a Singleton

Question

To begin with, I am NOT trying to create a subclass of a singleton class. (At least I'm sure I'm not trying to).

I have a class ClassA that is abstract.

I have two classes, ClassA1 and ClassA2 that extend ClassA.

I want ClassA1 and ClassA2 to be singleton classes. I could just write the code in each one to do so but I would prefer to write the code once in ClassA and reuse it in all of it's sub-classes. Is there a way to do this?

Answer 1

Probably not - the singleton pattern requires static methods/fields, which would be shared by ClassA and all its subclasses if defined in one place.

Answer 2

I would suggest private constructors for ClassA1 and A2 and having static methods for object creation. This way you have complete control over object creation. The book EffectiveJava details out the adavatages of this approach.