Needing Evidence on the Advantages of ABAP OO

Question

I am looking for the warm and fuzzy that I've yet to experience while being convinced about this one particular advantage of OO. Particulary involving multiple creation of objects, or instances occurring at one time.
I know the syntax of local and global classes, have done quite a bit of reading, and am familiar with OO coding, but seem to be missing the real-world implications of its use and its superiority to Function Modules in Function Groups.
My understanding is that with data in Function Modules within a Function Group, unlike attributes in a class, a single value in a field has one existence (and value) at runtime for the Function Group. However, for attributes, or objects, in a class, multiple instances may occur at one time. While even as I say this it confuses me, because I do not think I've seen an example of a convincing custom application in SAP in my experience only. Not that I do not doubt SAP's intent, I just am not getting it.
Can any experienced, and already convinced, ABAP OO programmer try to explain an application (in its simplest terms, if possible) where I would create multiple objects where this principle can be seen. And then tell me why I wouldn't be able to accomplish the same thing with Function Modules within Function Groups. Especially, if you have experienced a real-world implementation of this claim using OO.
What I would really like is to have some code that uses Function Modules, then some classes, that both accomplish the same results, that would prove to me that OO, and its classes are superior to Function Modules in Function Groups.I suppose what I really need is an application where multiple instances of the same object is being used, and its advantages.
I will listen to any, or all explanantions. I will accept any code, links, etc. Anything, please to settle my thinking and convince me once and for all.     
                                    Thank-You.
Edited by: TMM on Jun 17, 2009 4:36 PM
Edited by: TMM on Jun 17, 2009 4:37 PM

Answer 1

This is real world stuff:
After an application has been developed, it has happened a few times that I've wanted to use the same logic (or very similarl) in a different context.  By subclassing, I'm able to reuse what I've already developed, with little effort.  All I've had to do is redefine one or two methods of the main class.
I often develop stuff that has to run on different versions of SAP.  Subclassing here is very useful, as the subclass for ECC 6.0, for example, doesn't even have to pass syntax checking in 4.6c!
Using composition, I was able to develop an ["ABAP Decision" process type in BW|https://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/com.sap.km.cm.docs/library/uuid/30664504-40dd-2a10-3794-db7b4190bef3] - re-using what SAP developed.  The only coding I had to do was the variation from the standard sap.
I've developed a framework for writing Function Exits in BPS.  For a new function exit, I subclass the main class, and override an initialisation method and a processing method.  All the repeated stuff I was doing before is in the main class.
Generally, I find that developing in OO takes a little longer, but maintenance and support is much quicker.  As the bulk of the cost of software development lies in the latter, this can only be a good thing.  I also find that I'm reusing a lot of generic code I'm developing - e,g, I've developed a class for handling hierarchies in BW.
Currently, I'm working in the QM module, developing reports and smartforms for notifications.  The first thing I did was create a class ZCL_NOTIFICATIONS, which is my Data Access class, getting the various bits of data that I need in my reports.  This will be used in all my reports.  Now, I could do this using Function Modules, but using the functional notation of objects, I can say
l_physnum = lr_notif->get_physnum( ).
rather than
CALL FUNCTION MODULE 'GET_PHYSNUM' IMPORTING e_physnum = l_physnum.
I think the former is neater.  Also, if had a physnum in a different class, I can use the same name.  With function modules, I'd have to have
GET_PHYSNUM_FOR_NOTIFICATION
GET_PHYSNUM_FOR_INVENTORY
Finally, with CONSTRUCTOR and CLASS-CONSTRUCTOR, initialisation can be done without having to remember to call the INITIALISATION function module of my function group. 
matt