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Yeah, I guess my question is targeting the classes that might normally be created by an ORM. In our case, they are WCF data contracts, and have no behaviour.
The system also has other classes with behaviour, such as a UserBusinessManager class, that exposes methods for working with a User object, to perform actions like Load, Update, Insert, etc.
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Hi,
the situation is as follows:
There are 2 classes - C1 and C2 - both inherited from an abstract class A. The reason is that instances of C1 and C2 are to be stored in an inhomogeneous collection, and a common base class (A) is used to access their functionality (textbook polymorphism).
The abstract class A defines an abstract method M. This is meaningfully overriden in C1, but has no meaningful override in C2.
Common sense would suggest to remove it from the abstract class if either of its derived classes are unable to override it meaningfully.
However, the logic of the situation requires M to be defined in the abstract class A.
My questions are these:
1. Is it a sign of good or bad design to write empty abstract method overrides?
2. Is it a sign of good or bad design to write abstract method overrides that only throw an exception informing the user of an incorrect usage?
3. How common are the empty abstract method overrides in real-world programming practice?
Your answers are greatly appreciated!
Lukas
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Hi,
my 2 eurocents:
0. there is not only good or bad design, there is a continuum from very good to very bad
1. IMO overriding a method by an empty one because the functionality does not make sense is wrong.
2. throwing an exception in an override is OK
3. empty abstract overrides are only correct if that particular class needs a no-operation there; however I have never seen one.
4. FWIW, I would try and remove from the base class all functionality that is not meaningful for some of its decendents. If cats and dogs are mammals that eat and walk, and cats purr but dogs don't, then purr would not be a mammals method.
Luc Pattyn [Forum Guidelines] [My Articles]
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It seems like you have a list of things, and you want to go through the list and perform an action which is only relevant to some things in it. In this case you could consider exposing an interface, and then when you iterate thru the list you can use if(item is INeedToBeNotifiedAboutEclipses) ((INeed..)item).YoItsALittleDarkOutHere();
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Mark Churchill wrote: INeedToBeNotifiedAboutEclipses
No problem.[^]
Luc Pattyn [Forum Guidelines] [My Articles]
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We started getting requests to provide estimates for our development tasks, and I'm just wondering if there is a distinct breakdown into the technical design, implementation, and testing stages (from a developer's perspective) at other people's shops. If there is, I'd be curious to know what the ratios are (e.g. how much of the total development effort is spent on the technical design part, assuming you already have the preliminary specs?).
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Of course, you should divide your development task into several stages: preliminary/concept design (~15%), detailed design (~15%), implementation (55%) and unit test (~15%).
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If you have the requirements documented and putting aside the management and other support activities.
Technically the ration between System Design, Development and Testing is 25::50::25.
The Development will include Unit Testing.
This is a standard practice we follow for high level estimations... however the type of applications can make the ratio different.
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Hi,
I have started to learn UML, are there any good websites with samples? I started with use cases.
Regards
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Hi,
What are good software for UML diagrams? I would prefer cheap or free, but you guys can list any sort, commercial or free.
I tried Argo UML a while back, but not sure if it is efficiant for .NET 3.5?
Please let me hear your views.
Brendan
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Try StarUML[^] - it's free.
"WPF has many lovers. It's a veritable porn star!" - Josh Smith As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.
My blog | My articles | MoXAML PowerToys
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Thanks guys. Is it good software? Or average?
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StarUML is excellent. We use it to produce all of our design material through it's Word integration.
"WPF has many lovers. It's a veritable porn star!" - Josh Smith As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.
My blog | My articles | MoXAML PowerToys
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Pretty reasonable products they are, but as in all software, you have likes and dislikes, some you feel comfortable with, others not so and feel awkward. But try them out and come to your own conclusion.
ArgoUML is written using Java as is Visual Paradigm as is Oracle JDeveloper which includes some degree of UML. Star was written ( I think) with Delphi but as I recall, no longer being developed.
Sparx software via the link in my reply to your latest posting (above) is another paid-for product.
modified 1-Aug-19 21:02pm.
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If I need to sketch something quickly, I use Dia. It's lightweight, has most of the features I normally need, and it doesn't really matter if you're a Windows or a Linux user--you can get a build that fits either: http://live.gnome.org/Dia/Download[^]
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I have a method that could fail for a number of reasons, e.g. an invalid directory, a file not found in that directory, or an entry not found in that file. It's crossed my mind to throw different exceptions for the first two, and return null for the last, but this is not a good practice application of exceptions. My next alternative is to return null for any failure, but this makes unit testing the individual failures difficult. My third option is to return null for any failure, and set an ErrorMessage property on the class. If the method returns null, the caller can read this property and test/report on the error.
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Hi Brady,
IMO you should come up with satisfactory functional specs first, independent of future implementation and/or testing concerns. Once the specs are cast, you can worry about implementing and testing.
You shouldn't burden the user with a more difficult API just because that makes testing easier, should you?
So, will the class user want exceptions? will he be happy with a null return and the need to check something else to find what went wrong?
Luc Pattyn [Forum Guidelines] [My Articles]
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- the quality and detail of your question reflects on the effectiveness of the help you are likely to get
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Luc Pattyn wrote: So, will the class user want exceptions? will he be happy with a null return and the need to check something else to find what went wrong?
The class use is me. I'd prefer the latter, but was wondering if anyone had any caveats with that approach.
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Brady Kelly wrote: The class use is me
I thought as much, but it is rather irrelevant.
Brady Kelly wrote: but was wondering if anyone had any caveats
none here. It is somewhat similar to the Parse/TryParse situation.
They first offered Parse only, which throws whenever it feels like doing so.
Then came TryParse which doesn't tell you anything, except it returns a success flag.
I sometimes return a string, null=OK, non-null=error message (one step better than the old error number, 0=OK, negative=error; unless you need to check for a specific error that is).
Luc Pattyn [Forum Guidelines] [My Articles]
- before you ask a question here, search CodeProject, then Google
- the quality and detail of your question reflects on the effectiveness of the help you are likely to get
- use the code block button (PRE tags) to preserve formatting when showing multi-line code snippets
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Generally I'd go with throwing on any failure - it definitely leads to cleaner code (especially with errors bubbling up the stack and being handled at a convenient place). How you define "failure" then determines the behaviour.
"Entry not found in that file" would depend for me on your model. If every client must have a phone number then GetPhoneNumber(Client) should throw if there isn't one in the file. Either you are throwing an ArgumentException for an invalid client, or you are throwing because there is no phone number for the client - and *something* went wrong, which needs to be fixed.
If they might not have a phone number then returning null to indicate "none" is probably appropriate.
If it returns null when it detects an error, then you are moving the error detection to the client code, which is kinda silly. Theres probably lots of "client" code for the library - and this means you are duplicating a bunch of code. It also means you have created some pretty close coupling as well.
Whatever you do, make sure its clearly documented.
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If the conditions are exceptional then using exceptions is best practice.
If they are not exceptional then you might in some way encapsulate the problem, e.g., the result class, a success/failure flag and optional failure message string. This could be the messaging parameter rather than returning null.
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