SAX: ModSAX addition, general property query

Bill la Forge b.laforge at
Tue Mar 9 12:45:44 GMT 1999

From: John Wilson <tug at>
>I don't think that it's unreasonable to insist that objects representing a
>Feature, Handler or Property should either implement a distinct interface or
>subclass a distinct class. If this is so the Parser can tell what Feature,
>Handler or Property is being set by enquiring of the type of the object. (I
>favour insisting that they subclass distinct classes because (in Java) that
>naturally imposes the restriction that a single object can only represent a
>single Property.)

Filters often implement more than one (generally all) handler interface and
then register themselves with the underlying parser/filter for the same events
requested by the overlaying application/filter.

Your proposal would require the filter to instantiate seperate objects for each
set of events it needs to process, though it could simply pass-through the handlers
for those it does not.

The role and class of an object are often distinct. This was one of the things I
did not like about the aggregation scheme that was proposed by Sun a while back.
I think David got it right.


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