Enforce static Singleton from Abstract/Interface??

Question

Hi,
I'm trying to describe an interface IMyInterface which enforces all concrete subclass implementations to have a singleton "getInstance()" method whose method signature is always this "getInstance".
So declaring the interface
Interface IMyInterface{
public IMyInterface getInstance();
is fine, BUT in subclasses you can't override this method with a static class method.
ie.
public class X implements IMyInterface
private static X instance=null;
public static X getInstance()//ERR cannot override with static??
if( instance==null)
instance = new X()
return instance;
private X(){...}
I thought about using an abstract superclass but this doesn't strictly enforce subclasses to implement their own singleton class-method.
Why can't you override the method as a class-method?...and any ideas how to achieve this enforcement of the implementation of a singleton??

Answer 1

If you have an abstract base class with the method
public static Singleton getSingleton()  {
       return getSingletonImpl();
}where getSingletonImpl is an abstract method
protected abstract Singleton getSingletonImpl() ;This forces subclasses to provide an implmentation of the getSingletonImpl method.
However you cannot guarentee that the returned Singleton is actually a singleton
matfud