> Please either 
> 1) drop the throw() method entirely or
> 2) make throw an abstractmethod()

Ok, as I already said, I think it's important to provide the complete protocol as code will usually expect that. Also, close() has a helpful implementation, but it depends on throw(). Thus, I'll go with 2) and make throw() abstract. It's easy enough to call super(), but then it's explicit. I agree that that's better here.

Patch updated.