On Thu, 5 Feb 2004, Gary wrote:
> Tom:
>
> Thanks for your help.
>
> I originally added the factory creation code. At the
> time, I didn't realize I'd need a non-static method.
>
> The problem is that I have an abstract Factory class
> with an object creation method called something like
> newBusinessObjectInstance(). The abstract Factory
> class also has an abstract method defined called
> something like getBusinessObjectClass(). This latter
> method is implemented by the concrete factory
> subclasses (along with other methods), to let the
> abstract newBusinessObjectInstance() know what class
> to create.
>
> Since abstract methods cannot be static, I need to get
> an instance of the concrete Factory subclass.
>
> Clear as mud?
I can see your problem now. Initially I can think of two solutions:
1) "User-space" solution
It is likely that you use the factory as a singleton (or at least that it
could be used as one). In that case, the easiest (and most beautiful in
terms of design ;-) solution would be combination of strategy
(delegation) and singleton.
What I mean is that the factory class itself is a facade consisting of
static methods that delegate the actual creation to a singleton strategy
object (e.g. FactoryImpl) which then is a normal object (i.e. interfaces
and abstract classes can be used).
class Factory
{
private static FactoryImpl impl = DefaultFactoryImpl();
public static void setImpl(FactoryImpl newImpl)
{
impl = newImpl;
}
public static MyObject createMyObject()
{
return impl.createMyObject();
}
}
This makes the factory implementation pluggable though the interfacing is
static (thus no moving around of the factory object is necessary).
2) "OJB" solution
Change the implementation of the factory-class stuff somewhat as you
suggested:
* retrieve the factory method object
* if the method is static, simply call it
* if not, create an object of the factory class (using
Class.newInstance) and call the method on it
Could you please have a look as to whether the first solution would work
for you ?
Tom
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