abstraction

I would like to add a collection of objects to an arrayList ,only if the particular attribute is not null. I am thinking of extending the ArrayList and implementing the check inside the child class. One alternate way is to check for the the attribute before putting it in a Arraylist, but that would mean , i will have to scatter the if checks every where if i need to add the objects to the arraylist based on the logic. I would like to know your thoughts on it ... on a second thought is it a overkill ? Tomasz Nurkiewicz Decorator pattern I would actually recommend wrapping ArrayList using well

I am a Java programmer and am new to Clojure. From different places, I saw sequence and collection are used in different cases. However, I have no idea what the exact difference is between them. For some examples: 1) In Clojure's documentation for Sequence : The Seq interface (first coll) Returns the first item in the collection. Calls seq on its argument. If coll is nil, returns nil. (rest coll) Returns a sequence of the items after the first. Calls seq on its argument. If there are no more items, returns a logical sequence for which seq returns nil. (cons item seq) Returns a new seq where

First off, I think this is somewhat ridiculous to do but the other members of my team insist upon it and I can't come up with a good argument against it other than "I think it's dumb"... What we're trying to do is create a completely abstract data layer and then have various implementations of that data layer. Simple enough, right? Enter Entity Framework 4.1... Our end goal here is that the programmers (I do my best to stay only on the data layer) never want to have to be exposed to the concrete classes. They only ever want to have to use interfaces in their code, aside from obviously needing

In an object-oriented program: How much abstraction is too much? How much is just right? I have always been a nuts and bolts kind of guy. I understood the concept behind high levels of encapsulation and abstraction, but always felt instinctively that adding too much would just confuse the program. I always tried to shoot for an amount of abstraction that left no empty classes or layers. And where in doubt, instead of adding a new layer to the hierarchy, I would try and fit something into the existing layers. However, recently I've been encountering more highly abstracted systems. Systems where

With String.format , there seems to be a large opening for programmatic error that isn't found at compile-time. This can make fixing errors more complex and / or take longer. This was the issue for me that I set out to fix (or hack a solution). I came close, but I am not close enough. For this problem, this is more certainly over-engineered. I understand that, but I just want to find a good compile-time solution to this. More information can be found here. My question dealing with Basic Program 2 calculators. 1 Logic backend. Could be expanded to include other simple calculators. I wanted 1

I've read up on the Command Pattern, and I think I'm missing something. The Command object exists to abstract away the details of the Receiver object. It seems to me that we could simply stop here, and hold references to Command objects to execute the appropriate method at the appropriate time. Why, then, is the Invoker needed? What advantage does this additional indirection provide? We've already hidden the details of the Receiver behind the Command, what's the motivation for the Command to then be hidden from the client as well? Well, if you put it that way, it seems quite complex, but often

I am a java developer with good understanding of Object orientation concepts( or maybe, I think like that ). And right now I am learning design patterns (From Head first design patterns). I have been reading about OOPS concept abstraction to understand it briefly, and reading more about it has made me more confusing than I earlier was. As I understand, abstraction refers to hiding the internal details of the program while exposing the interface to other programmers without worries of internal details. But, I don't understand How abstract classes fit into this concept of abstraction, where