I sometimes end up with a class hierarchy where I have an abstract base class with some common functionality and a couple of implementing classes that fall into two (rarely more) groups which I want to treat differently in some cases. An example would be an abstract tree node class and different branch and leaf implementations where I want to distinguish branches and leaves at some point.
These intermediate classes are then only used for "is-a" statements in flow control and they don't contain any code, although I have had cases where they "grew" some code later.
Does that seem smelly to you? In my tree example, one alternative would be to add isLeaf() / isBranch() abstract methods to the base class and implement those on the intermediate classes, but that didn't seem to be any better to me, really, unless I'd mean to have classes that could be multiple things at once.
To me, using "is-a" tests in flow control is just as smelly as using switch/case. In a good OO design, neither is needed.
Yes, deep inheritance hierarchies are a code smell anyway.
Yup, definitely a code smell -- don't code these empty classes unless you're ready to write that code into it. Think YAGNI (you aint gonna need it) -- don't do it unless you need it already.
Also, have you considered cases wherein these classes are only there to provide abstract methods, or to group them based on capabilities in terms of methods or properties?
If that's the case, maybe what you really need are interfaces, not additional abstract classes?
In general, empty classes are a code smell.
I agree your isLeaf or isBranch methods are a correct alternative.
They add information about the objects , which is helpful.
(This is because, on the super class, you can't express that subclasses are "either leaf or branch").
The two methods with opposite results might also be considered as code duplication.
You could use only one... But I would recommend return an enumerated value LEAF or BRANCH.
A class that doesn't contain any code is definitely a code-smell....
Seems alright to me, if you're going to put new functionality in later.
But if not, an enum is generally used here.
-- Edit
Though I must agree with Ber, that you shouldn't generally be using 'is-a' anyway.
Related
I want to dispatch events to announce the progress of an asynchronous process. The event should contain 2 properties: work done and work total.
As the name suggests ;) i could use ProgressEvent; it has bytesLoaded and bytesTotal properties that i can use. However, my async process isn't loading bytes, its processing pixels, so the property names are a bit misleading for my use case - although the class name is perfect.
The alternative is to create a custom event with two properties that i can name how i like. But this means another class added to the code base.
So my question is; Is it better to reuse an existing class where the properties are suitable but maybe the naming isn't ideal; Or to create a custom class that perfectly fits the requirement? Obviously, one extra class is no big deal, but OOP is all about reusing stuff so adding an unnecessary class does make me uneasy.
I await your thoughts...
PS: This is my first question on stack so be gentle
For clarity, I'd create a new class. Adding a new class is not much overhead at all, especially for something simple like an event. I find that code is more readable when I don't have to make mental translations (like bytesLoaded really means pixelsLoaded). To me this is akin to choosing poor names for variables.
In addition, by going the other route and re-using the ProgressEvent class, I would feel compelled to document the code to indicate that we're dealing with pixels rather than bytes. That starts to get messy if you have a lot of classes that uses the event.
Re-use is great, but I'd opt for clarity as long as it doesn't impact your productivity or the app's performance.
writing in doc clearly, using custom event or ProgressEvent is well.
It's good to split code up into functions and classes for modularity / decoupling, but if you do it too much, you get really fragmented code which is also not good.
What is the golden rule for when to split code up into functions?
It really does depend on the size and scope of your project.
I tend to split things into functions every time there is something repeated, and that repetition generalized/abstracted, following the golden rule of DRY (Do not repeat yourself).
As far as splitting up classes, I tend to follow the Object Oriented Programming mantra of isolating what is the same from what is different, and split up classes if one class is implementing more an one large theoretical "idea" or entity.
But honestly if your code is too fragmented and opaque, you should try considering refactoring into a different approach/paradigm.
If I can give it a good name (better than the code it replaces), it becomes a function
I think you generally have to think of a chunk of codes have a chance of being reuse. It comes with experience to figure that out and plan ahead.
I agree with the answers that concentrate on reusability and eliminating repetition, but I also believe that readability is at least as important. So in addition to repetition, I would look for pieces of code (classes, functions, blocks, etc.) that do more than one thing.
If the name associated with the code does not describe what it does, then that is a good time to refactor that code into units which each have a single responsibility and a descriptive name. This separation of concerns will help both reusability, and readability.
Useful code can stick around for a long time, so it is important that you (or ideally someone else) can go back and easily understand code that was written months or years before.
Probably my own personal rule is if it is more than 2 lines long, and is referenced more than once on the same page (ASP.net), or a few times spread over a couple of pages, than I will write a function to do it.
I was taught that anything you do more than once should be a function. Anything similar should have a parent class, and above all else consult your source code "standards" within your organization. The latter mostly deals with formatting.
First, write the feature you're adding. (Notice the word "First", we tend to write a function/class before writing the feature, which might lead to having too many fragmentation).
Then, review the code you just wrote/changed, find what blocks of the code that is:
3-lines or more, and..
repeated, and..
Can be grouped under a named function. Because code is written by us, people (not programs), to be read/changed later by us, people (not programs).
Disclaimer: I'm trying to learn proper OO programming/design, so I'm pretty new to this stuff.
I guess this is a general design patterns question, but I'll base my example on a game engine or something that renders objects to the display.
Consider the following:
hierarchy http://img31.imageshack.us/img31/9633/diagrame.png
How can this sort of separation between physical objects (e.g., cubes, spheres, etc.) and the rendering mechanism be achieved in an extensible manner?
This design is not set in stone, and perhaps I've got something wrong from the start. I'm just curious as to how a problem like this is solved in real world code.
That would be the Adapter pattern, or it could be implemented as a Strategy pattern.
The renderer should not be extended by the objects which he is supposed to draw. (Just my opinion) an object in your world is NOT a renderer but the renderer uses objects.
So you have maybe:
Interface IRenderer which defines a function draw(BasicObject).
Then your objects just extend BasicObject to be handled by the/a renderer.
As I said just my opinion. :)
Strategy patern it is.
I would use a Visitor pattern here.
Where the Visitor is the renderer and were the Visited is the 3D/Object.
I would also make the 3D/Object a composite.
Lately I've been doing a lot of front-end work. Some developers here have been naming their elements things like "divPhotoGalleryContainer" and sometimes I'll just see "galleryContainer."
Is there a good naming convention? Is adding "div" really useful?
The stupid thing is, Hungarian notation like divPhotoGalleryContainer is totally unnecessary with CSS. You can name the ID PhotoGalleryContainer and target it to a <div> element in the CSS:
div#PhotoGalleryContainer {
/* rules */
}
Inside that rule you can usually assume certain properties like display: block, unless you're targeting generic divs somewhere else (kinda bad practice).
There aren't really any specific conventions for naming, just use names that are clear and simple.
I don't think it's particularly useful, but I don't think it's harmful either. Consistency is the most important convention.
The best naming convention is the one that makes sense to the developers/designers involved in the project. Given the two examples in your question, I'd be willing to bet that the "divPhotoGalleryContainer" contains "div" because either: it's referenced in a CSS selector, or some javascript code is looking at it and it's somehow helpful to know what type of element the id is referring to.
The "divPhotoGalleryContainer" convention seems like an HTML-ish flavor of Hungarian notation.
It is good to have a naming convention, because it will make you keep track of your elements and classes, and save you from having to read the html code to find out what element is named what. This will help you both when writing css and javascript. A good naming convention for an id should include:
a way to differentiate closely related elements, such as #passwordContainer from #passwordLabel and #passwordInput
structural names rather than presentational names, for example #main-content rather than #blue-square (as the color might change later). More info here: http://sixrevisions.com/css/css-tips/css-tip-2-structural-naming-convention-in-css/
a way to differentiate similar elements, for example on a page that lists different posts that have the same type of elements, you may name them #postContainer-43 and #postContainer-95 for post number 43 and 95 respectively, and give them the class .post or .postContainer
The most important thing is that you're consistant with whatever method you use.
However, I've always found it helpful to use the hungarian type notation of "divPhotoGalleryContainer", and "txtLastName". It makes it easier to distinguish page elements from other variables, both client and server side.
It's not harmful to add "div" in that case.
As DisgruntledGoat said, hungarian notation can be useless with CSS (that is, unles you don't want to restrict a class to one element type), and Rob's comment is right, you may even change your elements and keep the same classes/IDs, but, it may be helpful to understand the code better, lately.
I always use hungarian notation because I'm used to it. If you're used to something, keep it, as it's easier than changing it. In enviroinments where many coders are writing the same things, unless there is a convention, you may write as you want. However, being over-descriptive is not as bad as being under-descriptive. That said, I vote for comprehensive names for everything including variables, functions, classes, IDs, XML elements, etc. If it gets hard to read, use more/better placed spaces/lines. If it adds more than wanted to the file size, minify it.
I have problems with how to design some classes. I have three classes. One superclass, and two subclasses.
One subclass (AnimatedCharacter) is made by flash, and is used to display the object on screen. The other (CharacterPhysics) is made by myself to extend the superclass.
The problem is that the object I use, is of the type AnimatedCharacter, so I can't just put it in a variable of type CharacterPhysics.
What I tried is some sort of Decorator pattern, by giving the object of type CharacterPhysics a reference to the other object. But now I have to override all the methods of the superclass and pass the methodcalls to the reference. Not an ideal situation.
Does someone know how to solve this kind of problem?
alt text http://www.freeimagehosting.net/uploads/7a95f8352c.png
I don't quite understand the purpose of this class structure you describe (the class names confuse me), but in general a few things come to mind that might help you:
Almost always the best solution is to try and rethink your class model by evaluating whether you should for example break up the responsibilities of classes in an alternate way so that you could utilize inheritance and polymorphism in a better way.
"The problem is that the object I use,
is of the type AnimatedCharacter, so I
can't just put it in a variable of
type CharacterPhysics."
If you want to put an AnimatedCharacter into a variable of type CharacterPhysics, the former should extend the latter, or you should have a common interface (or superclass) for both and then type the variable as such. If this is not possible, my opinion is that you should probably try to rethink and refactor your whole class structure, assuming that you have a solid "object-oriented" reason for wanting to do this in the first place ;).
If the above is not possible, there are some other tricks you can evaluate in your context:
The use of mixins can work as a "poor man's multiple inheritance". Derek Wischusen has some examples on how to implement them in AS3 at flexonrails.net.
"Kind of" implementing the decorator pattern with flash.utils.Proxy. The problem with this approach is that you defer a lot of error checking from compile time to runtime, but the good thing is that you don't have to manually write the "proxying" implementations of all of the methods of the "decorated" object, but write just one (callProperty()) instead.
You can interpret a sublass as an instance of a superclass but not vice sersa. Did you state this backwards?
If so, you could use:
vas cp:CharacterPhysics;
...
var ac:AnimatedCharacter = cp As AnimatedCharacter
Off the top of my head, it seems like those 2 should be interfaces which your main class implements