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From: mark_lundquist@my-deja.com
Newsgroups: comp.lang.ada
Subject: Java packages (was Re: Do we need "Mission-Critical" software? Was:
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Date: Fri, 02 Feb 2001 06:45:23 GMT
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Date: 2001-02-02T06:45:23+00:00
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In article <3A64A94C.F265050A@ftw.rsc.raytheon.com>,
  Wes Groleau <wwgrol@ftw.rsc.raytheon.com> wrote:
>
> > Java wanted to have better namespace control, so Java has packages.
> > These are better than C++ namespaces and more like Ada packages. But
> > the encapsulation construct in Java is still the "class", and in at
> > least two important senses (there are several) of the value
> > of "separation of interface and implementation", Java classes fall
> > short,
>
> The fact that in Java, "package" is so closely coupled
to "subdirectory"
> shows that the Java designers had little understanding of the
> _difference_ between interface and implementation, so how could they
> see any reason to _separate_ them?

Hmmm, I think that may be a misapprehension on your part...

You're thinking of the directory structure of class files, which
follows the package hierarchy.  But that's an implementation detail;
the semantics of Java packages in no way depends on it.

And anyway, finding fault with Java packages for not being an
encapsulation mechanism is missing the point -- Java packages are not
supposed to be an encapsulation mechanism, they are strictly a
namespace control mechanism.  The encapsulation mechanism is the class,
and it fulfills the essential aspect of encapsulation (by means of
private members)...

> More evidence is in the fact that
> every primitive type declaration basically describes an implementation
> where most type definitions in Ada (at least in well-written Ada)
> emphasize the abstractions more than the implementations.

Yes... as I pointed out in the previous post, Java classes don't
provide separation of interface and implementation in some important
senses (those that have to do with textual separation).

Mark Lundquist


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