topic Re: Multiple Inheritence in Application Development and Automation Discussions

Multiple Inheritence

Former Member — Fri, 21 May 2010 14:42:25 GMT

Dear Friends,

Can You Tell me Multiple inheritence is possible using ABAP Objects, if Yes How?I thought We can't implement Multiple Inheritence in OBAP but We can implement Several Interfaces with in the Class?

Regards,

D.Kiran Kumar.

Re: Multiple Inheritence

Former Member — Fri, 21 May 2010 14:48:14 GMT

That's correct.. There is no multiple inheritance in ABAP, but a class can implement multiple interfaces for polymorphism.

Re: Multiple Inheritence

former_member776318 — Sun, 23 May 2010 07:29:42 GMT

Hi,

In terms of object oriented programming, there is a reason is reason why multiple inheritance cannot be supported by a pure Object-Oriented Language (for example Java, ABAP).

Consider you have two classes C1 & C2. Both the classes have a method. The name of the method is M. The signature of the method M (i.e. its importing/exporting parameters) is same in both the classes. But the internal implementation the method (i.e. the logic or the code inside the method) being different.

Now, if the multiple inheritance had been supported by ABAP, in that condition, if there is a class C3, which inherits from both classes C1 & C2 (i.e. C1 & C2 being the base class of the child-class C3). Then by the rule of inheritance, the child class should inherit the methods of its parent class. But, in this case, the system would not be able to determine from which of the parent class C1 or C2 should the method M be inherited to child class C3.

There is one more way to look at it. Suppose, if you call the method C3->M( ). The system will first try to find the method in class C3. When if does not find the method in C3, it will try to look for the method in the base class. But, in this case, the system would not be able to determine, which of the code C1->M( ) or C2->M( ) it should execute. This is just a logical explanation & this is the reason why multiple inheritance is not supported by a Pure Object Oriented language.

However, an object-based language like C++ supports Multiple inheritance.

Explanation for why multiple inheritance is possible through INTERFACES.

Consider you have two classes C1 & C2, both having a method as M with same signature. The only difference in this case is that the class C2 does not contain any definition (logic or code) for the method (i.e. it just defines the method but does not implement it). In this case, it would be clear to the system that the method M should be inherited from the base-class C1 to child-class C3 (since C2 does not contain any definition).

In this case, we do not call the class C2 as a class but it is an INTERFACE. If you would have some idea Java, you would know that an interface is a Pure Abstract Class i.e. a class, which contains only the declarations for the methods but no implementations for any of the methods.

Hope that helps you understand why you are able to implement several interfaces along with one single Base-Class into a child-class.

Let me know if you have any query regarding the same.

Regards,

Saurabh

Edited by: Matt on May 24, 2010 9:30 AM - correct formatting

Re: Multiple Inheritence

Former Member — Sun, 23 May 2010 08:55:27 GMT

@Kiran: I recommend for simple questions like this to take a quick look at the ABAP help. It's rather trivial to get to the explanation for [inheritance|http://help.sap.com/abapdocu_70/en/ABENINHERITANCE.htm] and see this:


ABAP Objects applies the principle of single inheritance.

Following the link on [inheritance and interfaces|http://help.sap.com/abapdocu_70/en/ABENINHERITANCE_INTERFACES.htm] will tell you


The classes of an inheritance tree can implement any number of interfaces but each interface can be implemented only once in each inheritance tree.

@Saurabh, let's try to keep our facts straight. You basically describe the [diamond problem|http://en.wikipedia.org/wiki/Diamond_problem], but come to a wrong conclusion. [Multiple inheritance|http://en.wikipedia.org/wiki/Multiple_inheritance] is possible and used by (some) [OOP|http://en.wikipedia.org/wiki/Object-oriented_programming] languages (and those which don't have it often have similar features like [mixins|http://en.wikipedia.org/wiki/Mixin] etc.). It's simply a design choice if a language should support multiple inheritance or not and if yes, how to resolve a method call.

Cheers, harald

Re: Multiple Inheritence

Sandra_Rossi — Sun, 23 May 2010 16:58:56 GMT

Hi Harald, sorry to bother you in that thread, do you know how I can watch your posts (it's really a pleasure to learn from you!) I can for Thomas Jung, Otto Gold, Rob Burbank, etc., but not you, unfortunately.

Re: Multiple Inheritence

matt — Mon, 24 May 2010 07:32:47 GMT

Harald would have to switch on the ability to be watched himself.

Re: Multiple Inheritence

Former Member — Mon, 24 May 2010 07:52:31 GMT

Sorry, had set at some point the option Allow other users to watch me to No, because I felt embarrassed that people might find out that my [BS|http://wordnetweb.princeton.edu/perl/webwn?s=****]-to-valuable-posting-ratio is awfully high (and without a specific watch it's easier to hide among the other silly postings). Anyhow, if you're willing to ignore/skip over the crap, I've now changed my settings...

Cheers, harald

p.s.: It actually drove me nuts, because I first couldn't find the setting. I kind of suspected that it's in the Your watches section, but here I almost always get a gateway timeout (maybe I should delete some or SAP should somehow speed up the query). I've tried this from time to time over the last twelve hours and only now it succeeded.

Re: Multiple Inheritence

Sandra_Rossi — Mon, 24 May 2010 10:55:40 GMT

Formidable Harald, I can now watch your answers, and I'll be glad to see your silly answers, just to prove that you're human

About the watches, I have the same problem, I need about 100 attempts (!!), and I unwatch all old watches from time to time.

Re: Multiple Inheritence

Former Member — Thu, 27 May 2010 09:10:23 GMT

However, unlike C++, ABAP Objecs support only single inheritance. Because it is Confusion to base Class

access the instance methods of the two Super Classes.

Using Interfaces we can implement multiple inheritance concept in ABAP like in JAVA.