http://en.wikipedia.org/wiki/Visitor_pattern
--- On Wed, 11/26/08, BJ Freeman <[EMAIL PROTECTED]> wrote:
> From: BJ Freeman <[EMAIL PROTECTED]>
> Subject: Re: Discussion: Screen Widget Java Code Cleanup
> To: dev@ofbiz.apache.org
> Date: Wednesday, November 26, 2008, 6:50 PM
> where can I find out about the visitor model
>
> Adrian Crum sent the following on 11/26/2008 6:05 PM:
> > I would like to work on cleaning up the screen widget
> Java code. Here are some of my ideas:
> >
> > 1. The screen widget model classes are trying to be
> too many things. As a result, they contain some messy and
> scary code. I'd like to see the model widget become more
> of a data structure, and move the rendering code into the
> rendering classes.
> >
> > 2. Use a true visitor pattern in the model widgets.
> The current pattern is what I would call "befuddled
> double dispatch with baggage." Methods like
> >
> > public void renderWidgetString(Appendable writer,
> Map<String, Object> context, ScreenStringRenderer
> screenStringRenderer)
> >
> > would become
> >
> > public void accept(ScreenWidgetVisitor visitor).
> >
> > Rendering classes would implement the
> ScreenWidgetVisitor interface. The model widgets won't
> need to be concerned with writers, contexts, or any other
> messy details.
> >
> > 3. Convert the existing artifact gathering code to a
> screen widget visitor. That would get the artifact gathering
> code out of the model widgets and put it where it belongs.
> It would probably simplify the artifact gathering code as
> well.
> >
> > Once these steps are completed, the model widget
> classes will be simple immutable data structures. The only
> code most of the model classes will have is a constructor
> and the accept method.
> >
> > The rendering code will be simplified, since there
> will be better separation of concerns.
> >
> > I will probably start off with #1 - move the rendering
> code from the model classes to the rendering classes. Once
> the dust settles from that, I will introduce the visitor
> interfaces and visitor classes. The existing model methods
> will be deprecated. The model classes will be bloated while
> they support both patterns. When the time is right we can
> remove the deprecated methods and we'll have lean, well
> structured screen widget code.
> >
> > What do you think?
> >
> > -Adrian
> >
> >
> >
> >
> >
> >
