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   Re: ANN: SAX 2.0 extension proposals.

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  • From: David Brownell <david-b@pacbell.net>
  • To: David Megginson <david@megginson.com>
  • Date: Mon, 28 Feb 2000 21:06:30 -0800

David Megginson wrote:
> David Brownell writes:
>  > David Megginson wrote:
>  > >
>  > > David Brownell <david-b@pacbell.net> writes:
>  > >
>  > > > However, I do wonder what you think about the fact that this will
>  > > > need to run in environments where calls like System.getProperty()
>  > > > aren't allowed, or which may not support dynamic loading.
>  > >
>  > > Suggestions?
>  >
>  > Same approach used in classes like "java.lang.System" -- the API has
>  > static class methods, but implementation of the class is unspecified.
>  > It varies between environments; the reference implementation can be
>  > changed.
> That's not a good parallel, though, because there's always only one
> java.lang.System class in any given Java installation (as far as I
> know) 

Any given class loader has only one implementation of a class, true.

But my point is that this is for supporting adequate defaulting
in _any_ Java environment.

>	-- on the other hand, if I install a future version of both
> IBM's XML4J and James Clark's XP (for example) into the same Java
> installation, then I would get two different versions of
> org.xml.sax.helpers.XMLReaderFactory and whichever happens to be first
> on the classpath will always get hit.

Which would be absolutely no problem, and might even be a benefit.

If you care about which parser you get, then ask for it.  Else
you asked for a default, and you got one.  Anyone who can control
a system property can do the same to a class path, but the converse
isn't true.  Software setting up a controlled environment for running
components (a preferred model) will assemble it at runtime using
class loader primitives and such, but can't set system properties

- Dave

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