OO Design Patterns Decorator in ABAPI am happy bunny to see more and more blogs on SDN about object orientated programming in ABAP. Even after 1. 2 years OO is still struggling to gain traction in the ABAP community so the more the merrier. My mate Matt Harding asked the other day why do we still have procedural programmers out there I would say they are still in the vast majority. So I get my head around that, we need a separate database access layer so we can change the way we get data and the other parts dont care, we need a separate user interface layer so we can swap ALV for Web Dynpro or UU5 or whatever comes next and the rest of the architecture does not care etc. I thought I had it nailed. I would, I thought, write programs which would look like this I am changing the analogy a bit, but the separations of concerns is still there. Then we get into unit testing, and the idea of mocking up layers like the database and the user interface, and injecting them into the constructor of the main class. Again, after a while I understand all this, the last piece of the puzzle as I asked Uwe in the above blog is why do we inject using an INTERFACE as opposed to a subclass of the class we are mocking He tried to explain it to me, but Im dumb, so I had to do some more investigation. And the light bulb finally came on. Initially I just could not see the point of interfaces abstract definitions of method names and interfaces with no code behind them but then suddenly Im through the looking glass and I could no longer see how you could live without them. The important bit that got through to me is that you shouldnt be using an interface for mocking objects in unit testing, you should be using interfaces all over the place as a matter of course. Someone said that in a comment at the end of my very first blog in SDN when I started talking about subclasses, but at that point it went right over my head. My farm example would then look more like this The attributes would be tables now instead of single object references, but then the farm does not know or care what humans live upon it, what animals are in the farm, or what vehicles are used, or the exact details of how they do what they do, the farm just sets the high level requirements and leaves the classes to carry these out as they see fit. This means we can add animals and vehicles and the farmer can run off with Postman Pat leaving the wife running the farm, and the main class doesnt need changing. It is the same with a database access layer class, if the client only accesses it through its interface you can make radical changes, even substitute another class entirely that implements the same interface and the client neither knows nor cares. 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Head First Design Patterns C PdfNow, some of this may seem random or incomprehensible, as it did to me not so long ago, and indeed as much of OO world still does, so the way I crawl along is to isolate one concept at a time, from the most interesting article I read at the time, and try and replicate this in ABAP first as a generic example like you see in the articles, and then ask the difficult question which is can this REALLY be useful. If you have colleagues who feel OO is the devils work then that last question is the million dollar one. Here is a question that occurred to me once I locked on to what interfaces are for If these are so useful, then presumably all classes should expose their public methods as an interface, and no clients should ever hold references to them any other way. Now, like all blanket statements that cant possibly be true, so can anyone explain why not Any takers In the meantime, I read a good article the other day on the Decorator pattern so that is next cab off the rank to try and replicate in ABAP and then try and find a realistic use case. You may ask since this is the title subject of the blog then why have I been waffling on about interfaces and the likeIn a clever twist this will all come together at the end, just like Snoopy and his novel It was a Dark and Stormy Night. Decorators. Of all the patterns described, the only one I was really struggling to see the practical benefit of was the Decorator. As I may have said before, even if the OO concepts are clearly better than procedural ones, it is easy to get so caught up that you just say this is better because it is. Here is an extract from Asterisk the Gaul where the exact same thing is going on. Centurion Crismus Bonus has just drunk what he thinks is the magic potion to give him superhuman strength, but he has not really. You could say that OO programming and design patterns are the magic potion and that big rocks are business problems that need to be dealt with using the superhuman strength these tools give you. From the book I was plugging, in regard to the decorator pattern The inference is that it is clearly impossible to add another instruction saying the name with just one line of code without OO and design patterns. You just cant do it in procedural programming Or maybe I can PERFORM SPEAK USING HELLO. PERFORM SPEAK USING HOW ARE YOU DOING. Pinball Hall Of Fame Ps2 Iso Free. Now how would I add the extra instruction with just one line of code, in my procedural world Any ideas Oh dear, someones just dropped a rock on my foot. I am being really unfair here, but now that I am convinced this OO is a really good thing, at least in principle, I have a mission to try and spread the word. Another example of the decorator pattern comes in the sample chapter from another great book series called head first which tries to provide an idiots guide to OO design and programming in an entertaining way. The way they present the material is what I like best, it is all jokes and silly examples, but everything is technically valid. Now why would I like that So, I will do a quick translation of their example into ABAP, using a slightly different concept, and then we can start the debate. The first problem I have is how to paste the ABAP code into the SCN. There are several ways, most of which mangle it beyond recognition, some of which make it look OK on the screen but you cant print it as it vanishes when turned into a PDF or formats itself into one big line, whereby you see only the first few characters. Ie Screenshot Pro Serial. Am I the only one who has noticed this So, first the easy bit, the translation from Java to ABAP, and then the difficult bit, which is to actually THINK about this, and find a use for the concept. The head first example uses types of coffee, which are then decorated by subclasses representing the various things you can put into coffee like milk and chocolate and the like. Naturally I could not use the same example, that would be BORING, so I tried to think of another product which has different things inside it, and since I seem to spend an inordinate amount of time in hotels, I thought that would do. They have different brands for different income groups and each can contain a mixture of features like pools or bars or what have you. Also, in the same way you can have two shots of something in a coffee you can have two bars inside a hotel. I should write the unit test first and go backwards as that is what all the articles tell me to do. If you have read any of my recent blogs you will guess I am going to go totally bonkers on this, and use a whole bunch of helper classes just to make the unit tests look like plain English and thus be executable specifications.