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From: fjh@murlibobo.cs.mu.OZ.AU (Fergus Henderson)
Subject: Re: Eiffel and Java
Date: 1996/11/02
Message-ID: <55fhfu$8p0@mulga.cs.mu.OZ.AU>#1/1
X-Deja-AN: 193950815
references: <550sm2$sn1@buggy.news.easynet.net> <E00t53.CG2@syd.csa.com.au>
 <55562c$nkd@mulga.cs.mu.OZ.AU> <55ffdb$cki@bagan.srce.hr>
organization: Comp Sci, University of Melbourne
newsgroups: 
 comp.lang.eiffel,comp.lang.ada,comp.lang.sather,comp.lang.java.advocacy
Date: 1996-11-02T00:00:00+00:00
List-Id: <comp.lang.ada>


dbudor@zems.fer.hr (Darko BUDOR) writes:

]Fergus Henderson (fjh@mundook.cs.mu.OZ.AU) wrote:
]: Suppose I have two existing library classes (perhaps supplied by different
]: vendors) which have some commonality, but don't inherit from a common
]: base class.  In Sather, one can simply create a new interface and
]: declare these classes to be instances of this interface, without
]: modifying the existing code.
]: 
]: (Is that possible in Java?)
]
]Yes, it is.

If your code below is the only way of doing it, then I would say that
it *isn't* possible in Java.  The code below doesn't do the same
thing as the Sather code -- it has significant disadvantages.

]Suppose you have 2 classes from different vendors, class A and
]class B, with common methods void foo() and void bar(). You can declare an
]interface for common methods:
]
]public interface common {
]	public void foo();
]	public void bar();
]}

Fine so far...

]Now declare 2 new classes:
]
]public class MyA extends A implements common {
]	/* need constructors */.
]};

Disadvantage number one: you have to manually delegate all the constructors.
That is tedious and causes maintenance difficulties when someone later adds
new constructors for A.

]and use MyA and MyB instead of A and B.

Disadvantage number two: you can't use the new interface on the
original types.  This is *really* bad news.  It basically means is that
you can't use this method when interfacing with existing code that uses
A and B rather than MyA and MyB.

--
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.