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From: fjh@mundook.cs.mu.OZ.AU (Fergus Henderson)
Subject: Re: Eiffel and Java
Date: 1996/11/12
Message-ID: <5694r8$c9c@mulga.cs.mu.OZ.AU>#1/1
X-Deja-AN: 195925904
references: <328592FC.64F26D66@sede.unijui.tche.br>
 <1996Nov11.142547.4810@schbbs.mot.com>
organization: Comp Sci, University of Melbourne
newsgroups: 
 comp.lang.eiffel,comp.lang.ada,comp.lang.sather,comp.lang.java.advocacy
Date: 1996-11-12T00:00:00+00:00
List-Id: <comp.lang.ada>


shang@corp.mot.com (David L. Shang) writes:

]Separation of the interface from implementation is a good thing.
]It is required by the practical software engineering needs to reduce
]the dependency among software components. 
[...]
]But separation subtype from subclass is not.

Why not?  Doesn't this also serve to "reduce the dependency
among software components"?

]In Sather, implementation classes are not always subtype of the
]parent class. They merely reuse the code (inherite the implementation)
]defined in their parent, but not necessarily be subtype of it.
]Without subtyping, the interface provided in the parent cannot
]serve as a polymorphic interface for all the implementations.

Yes, and that's a good thing, isn't it?
It decouples the interface and the implementation,
making it easier to use a different implementation.

]In Java, implementation classes are always subtype of the
]interface class, but they cannot reuse the code in the interface
]class, because there is no implementation in the interface.

So the code is elsewhere, big deal.  They can still
reuse it, can't they?

--
Fergus Henderson <fjh@cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
PGP: finger fjh@128.250.37.3         |     -- the last words of T. S. Garp.