Re: RPG,COBOL or JAVA -- MIDRANGE-L



David Morris wrote:
>I do agree that RPGIV is lacks many basic features of
>an object oriented language.  Primarily the interfaces
>provided do not allow very much flexibility.  You cannot
>pass variable type parameters, and because of parameter
>passing restrictions, you cannot simulate inheritance
>directly.  In order to support these things you have to
>define your own storage system.  RPGIV will do little to
>help you understand OO, but I think it is a better
>starting point than RPGIII.

Agreed.  What RPG IV offers over RPG III is better
facilities for modular programming, and that's
certainly one step on the road towards OO.

>I am interested to find out how your experience with OO
>programming progresses.  We had problems when we
>assumed that inheritance should be used wherever
>possible.  We ended up backing off quite a bit.  I
>suspect this has happened to others.

Well, as part of my learning process, I'm currently
working on a genealogy app in my spare time.  This
is another of my many interests, and since there are
few genealogy apps that run on my chosen O/S, Linux,
it also has a practical use.  It's also a domain that
lends itself nicely to OO design.

I can relate to your experience regarding inheritance.
It's tempting at first to use it everywhere, even
where it's not appropriate.  One nice thing about OO
is that it really seems to force you to do things
right.  In particular, spending more time upfront in
the design phase helps tremendously.  When thinking
about inheritance, you need to examine the relationships
between your objects.  These relationships generally are
of two types:  "IsA"  and "HasA". For example, a dog
"is an" animal, but a dog "has" four legs.  This example
is obvious, but in practice, other relationships may not
be, especially when you're starting out.  Experience is
a good teacher.

>I am no expert in Java and I am sure most of our problems
>with OO have been caused by a lack of experience.   I
>have been working on a system that uses  inheritance
>extensively, and there were drawbacks.  One problem
>is that inheritance is defined at compile time.  Another
>problem, and the one caused the most problems for us
>was that changes to a parent can affect subclasses.
>A system built of components is generally more flexible,
>the trade-off is that you do not get the same level of
>re-use.

I've been there too!  Sometimes I really wish Java
supported multiple inheritance.  But then again, that
would only encourage patchwork application designs (IMHO).

I think OO is leading us to a level of software practice
where we do what's right not because we're told to, but
because we know it's right.

Cheers!  Hans

Hans Boldt, ILE RPG Development, IBM Toronto Lab, boldt@ca.ibm.com


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