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• Problem understanding Inheritance

  - by dhruvbird

  I've been racking my brains over inheritance for a while now, but am still not completely able to get around it. For example, the other day I was thinking about relating an Infallible Human and a Fallible Human. Let's first define the two: Infallible Human: A human that can never make a mistake. It's do_task() method will never throw an exception Fallible Human: A human that will occasionally make a mistakes. It's do_task() method may occasionally throw a ErrorProcessingRequest Exception The question was: IS an infallible human A fallible human OR IS a fallible human AN infallible human? The very nice answer I received was in the form of a question (I love these since it gives me rules to answer future questions I may have). "Can you pass an infallible human where a fallible human is expected OR can you pass a fallible human where an infallible human is expected?" It seems apparent that you can pass an infallible human where a fallible human is expected, but not the other way around. I guess that answered my question. However, it still feels funny saying "An infallible human is a fallible human". Does anyone else feel queasy when they say it? It almost feels as if speaking out inheritance trees is like reading out statements from propositional calculus in plain English (the if/then implication connectives don't mean the same as that in spoken English). Does anyone else feel the same?

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• How to restrict user from modifying data in mysql data base?

  - by Paul

  We need to deploy application(developed by Java) WAR file in client place which make use of MySql 5.0. But we would like to restrict the user from modifying any data in the database. Is there any way to protect data. The client can make use of the application but they should not be able to change any value in database. How to do that?

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• Is it okay to violate the principle that collection properties should be readonly for performance?

  - by uriDium

  I used FxCop to analyze some code I had written. I had exposed a collection via a setter. I understand why this is not good. Changing the backing store when I don't expect it is a very bad idea. Here is my problem though. I retrieve a list of business objects from a Data Access Object. I then need to add that collection to another business class and I was doing it with the setter method. The reason I did this was that it is going to be faster to make an assignment than to insert hundreds of thousands of objects one at a time to the collection again via another addElement method. Is it okay to have a getter for a collection in some scenarios? I though of rather having a constructor which takes a collection? I thought maybe I could pass the object in to the Dao and let the Dao populate it directly? Are there any other better ideas?

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• What exactly is GRASP's Controller about?

  - by devoured elysium

  What is the idea behind Grasp's Controller pattern? My current interpretation is that sometimes you want to achieve something that needs to use a couple of classes but none of those classes could or has access to the information needed to do it, so you create a new class that does the job, having references to all the needed classes(this is, could be the information expert). Is this a correct view of what Grasp's Controller is about? Generally when googling or SO'ing controller, I just get results about MVC's (and whatnot) which are topics that I don't understand about, so I'd like answers that don't assume I know ASP.NET's MVC or something :( Thanks

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• Programming DataEntry&Forms: Population of Official Common Data Lists

  - by rlb.usa

  As a programmer of data-entry forms of all kinds, I often find myself making fields for things like Country and State. Consider: Perhaps a list the 50 United States names is an easy thing to find (does one include DC?) , but the countries are not. Nearly every site you find has a differing list with all of the political goings on over the years, and they become outdated quickly. What's the best practice regarding population of these kinds of lists? Is there an official list somewhere that one uses to populate these kinds of formal/official fields? Where do you get this data from, when it's not exactly specified in the specs?

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• Best practice for avoiding locks on a heavily read table?

  - by Luiggi

  Hi, I have a big database (~4GB), with 2 large tables (~3M records) having ~180K SELECTs/hour, ~2k UPDATEs/hour and ~1k INSERTs+DELETEs/hour. What would be the best practice to guarantee no locks for the reading tasks while inserting/updating/deleting? I was thinking about using a NOLOCK hint, but there is so much discussed about this (is good, is bad, it depends) that I'm a bit lost. I must say I've tried this in a dev environment and I didn't find any problems, but I don't want to put it on production until I get some feedback... Thank you! Luiggi

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• Is it a good idea to create an interface for each domain objects?

  - by Amitabh

  I was just looking into the source code of an existing project which uses nHibernate and found that there are interfaces created for each entity classes. E.g ICustomer for Customer class. I was just wondering what can be the advantage of this pattern as ICustomer contains mainly the properties and very few methods.

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• Session vs singleton pattern

  - by chobo

  Hi, I have a web application where I would like to pull user settings from a database and store them for Global access. Would it make more sense to store the data in a Singleton, or a Session object? What's the difference between the two? Is it better to store the data as an object reference or break it up into value type objects (ints and strings)? Thanks!

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• How do you remove/clean-up code which is no longer used?

  - by clarke ching

  So, we have a project which had to be radically descoped in order to ship on time. It's got a lot of code left in it which is not actually used. I want to clean up the code, removing any dead-wood. I have the authority to do it and I can convince people that it's a commercially sensible thing to do. [I have a lot of automated unit tests, some automated acceptance tests and a team of testers who can manually regression test.] My problem: I'm a manager and I don't know technically how to go about it. Any help?

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• does anyone see any issues with this thread pattern?

  - by prmatta

  Here is a simple thread pattern that I use when writing a class that needs just one thread, and needs to a specific task. The usual requirements for such a class are that it should be startable, stopable and restartable. Does anyone see any issues with this pattern that I use? public class MyThread implements Runnable { private boolean _exit = false; private Thread _thread = null; public void start () { if (_thread == null) { _thread = new Thread(this, "MyThread"); _thread.start(); } } public void run () { while (_exit) { //do something } } public void stop () { _exit = true; if (_thread != null) { _thread.interrupt(); _thread = null; } } } I am looking for comments around if I am missing something, or if there is a better way to write this.

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• Open-source: licence header on each source file OR a single COPYING OR both?

  - by systempuntoout

  Publishing an open-source project, is it enough to add a COPYING file to the package or do i need to copy and paste it on top of every project's source file? On public repository like github or google code i saw mixed things and i'm curious on how this legal aspect should be handled correctly.

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• Will this be garbage collected in JVM?

  - by stjowa

  I am running the following code every two minutes via a Timer: object = new Object(this); Potentially, this is a lot of objects being created and a lot of objects being overwritten. Do the overwritten objects get garbage collected, even with a reference to itself being used in the newly created object? I am using JDK 1.6.0_13. Thanks for the help.

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• More swing design & actions

  - by takoi

  Im pretty new to gui programming so i've been reading through every post on this site about swing and design. Whats been answered over and over again is that one should have a class which handles all the action. Like this: (GUI being some JFrame) Now, this works great for one-way actions, like OpenDialog. But the actions for buttons in DialogA and B will have to have access to all the components (there will be many) in its dialog, and the controller. This is where im stuck. The only sane way i can see is to put it in DialogA/B but i would then need to pass the controller all the way down, through classes that dont even need it, and it'll get all spaghetti. Really dont want that. Someone must have encountered this problem before. So where should i put this Action? Or should i just drop the whole design?

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• Need help in sorting the programming buzz-words

  - by cwap

  How do you sort out the good buzz from the bad buzz? - I really need your help here :) I see a lot of buzz-words nowadays, both here on SO and in school. For example, we had a teacher who everyone respected, who said "be careful about gold-plating and death-by-interfacing". Now, everyone and their mama cries whenever I'm creating an interface.. Another example would be here on SO where lately "premature optimization is the root of all evil", so everytime someone asks a perfomance question, he'll get that sentence thrown in his face. A few months ago I remember it was all about NHibernate in here, etc., etc... These things comes and goes, but only the good buzz stays. Now, how do you seperate the good from the bad? By reading blogs from respected persons? By trying to come to a conclusion on your own, and then try to convince others that you're right? By simply ignoring it?

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• Efficiently store last X items in an MySQL Database

  - by Saif Bechan

  I want to store the last 3 items in an MySQL database in an efficient way. So when the 4th item is stored the first should be deleted. The way I do this not is first run a query getting the items. Than check what I should do then insert/delete. There has to be a better way to do this. Any suggestions?

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• What is your the worst program/project you have done so far in your programming career?

  - by Bragaadeesh

  Few years before, I attended an interview for a company. I was given a programming assignment and I wrote a code which I thought at that time was perfect. But now after 3 years when I look back, I cannot find a more horrible code than that. Not to indulge in a lengthy subjective argument. But I would like to know what is the worst set of code you've developed/written?

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• When to use structs instead of classes?

  - by Earlz

  In C# when do structs make more sense to use than classes? What are some example scenarios? When should structs never be used?

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• Factory Method Using Is/As Operator

  - by Swim

  I have factory that looks something like the following snippet. Foo is a wrapper class for Bar and in most cases (but not all), there is a 1:1 mapping. As a rule, Bar cannot know anything about Foo, yet Foo takes an instance of Bar. Is there a better/cleaner approach to doing this? public Foo Make( Bar obj ) { if( obj is Bar1 ) return new Foo1( obj as Bar1 ); if( obj is Bar2 ) return new Foo2( obj as Bar2 ); if( obj is Bar3 ) return new Foo3( obj as Bar3 ); if( obj is Bar4 ) return new Foo3( obj as Bar4 ); // same wrapper as Bar3 throw new ArgumentException(); } At first glance, this question might look like a duplicate (maybe it is), but I haven't seen one exactly like it. Here is one that is close, but not quite: http://stackoverflow.com/questions/242097/factory-based-on-typeof-or-is-a

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• SQL - when should you use "with (nolock)"

  - by Andy White

  Can someone explain the implications of using "with (nolock)" on queries, when you should/shouldn't use it? For example, if you have a banking application with high transaction rates and a lot of data in certain tables, in what types of queries would nolock be okay? Are there cases when you should always use it/never use it?

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• My User control belonging to which Design Pattern??

  - by prashant

  Hello, I am creating a reusable component in C#.net. For that i have started a Control Library project and added a Control. Class MyControl : Control{} My user control just displays some images which will be used in many Windows Applications. Can you please tell me which design pattern i am using here. I am unable to decide which pattern they belongs. Thanks

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• Should the program logic reside inside the gui object class or be external to the class?

  - by hd112

  I have a question about how to structure code in relation to GUI objects. Suppose I have a dialog that has a list control that has a bunch of names obtained from a database. The user can edit the names. Does the logic reside inside that dialog class or should it be from the outside. To illustrate what I mean, here’s some pseudo code showing the structure of the code when the logic is handled outside the dialog class: NamesDialog : wxDialog { Private: ..stuff.. Public: ... SetNames(wxStringArray names); wxStringArray GetNames(); ..stuff.. } So the user of the class would do something like: wxStringArray names = DatabaseManager::Get()->GetNames(); names.Sort(); NamesDialogObject.SetNames(names); NamesDialogObject.ShowModal(); wxStringArray modified_names = NamesDialogObject.GetNames(); AddToDatabase(modified_names); //or something like this. On the other hand, the database logic can reside inside the NamesDialog class itself. In the show method I can query the database for the names and as the user interacts with the controls (list control in this case), the database can be updated from the event handlers. As a result the NamesDialog class only has the Show() method as there is no need to use SetNames or GetNames() etc. Which method is generally preferred? I don’t have much work experience so I’m not sure which is the proper way to handle it. Sometimes it's easier to handle everything in the class but getting access to objects it interacts with can be challenging. Generally can do it by having the relevant objects be singletons like the database manager in the above example.

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• Tracking user changes in ASP.NET MVC

  - by Ian Roke

  I have a requirement to track what authenticated users change with regards to the data when logged in. I don't need to track what pages they look at although that could be very useful in future. I have thought about saving the User Guid but that seems very clunky. Are there other methods/best practises?

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• Setting the type of a field in a superclass from a subclass (Java)

  - by Ibolit

  Hi. I am writing a project on Google App Engine, within it I have a number of abstract classes that I hope I will be able to use in my future projects, and a number of concrete classes inheriting from them. Among other abstract classes I have an abstract servlet that does user management, and I hava an abstract user. The AbstractUser has all the necessary fields and methods for storing it in the datastore and telling whether the user is registered with my service or not. It does not implement any project specific functionality. The abstract servlet that manages users, refers only to the methods declared in the AbstractUser class, which allows it to generate links for logging in, logging out and registering (for unregistered users). In order to implement the project-specific user functionality I need to subclass the Abstract user. The servlets I use in my project are all indirect descendants from that abstract user management servlet, and the user is a protected field in it, so the descendant servlets can use it as their own field. However, whenever i want to access any project specific method of the concrete user, i need to cast it to that type. i.e. (abstract user managing servlet) ... AbstractUser user = getUser(); ... abstract protected AbstractUser getUser(); (project-specific abstract servlet) @Override protected AbstractUser getUser() { return MyUserFactory.getUser(); } any other project specific servlet: int a = ((ConcreteUser) user).getA(); Well, what i'd like to do is to somehow make the type of “user” in the superclass depend on something in the project-specific abstract class. Is it at all possible? And i don't want to move all the user-management stuff into a project-specific layer, for i would like to have it for my future projects already written :) Thank you for your help.

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• Generating new tasks in a foreach loop

  - by Scott Chamberlain

  I know from the codeing guidlines that I have read you should not do for (int i = 0; i < 5; i++) { Task.Factory.StartNew(() => Console.WriteLine(i)); } Console.ReadLine(); as it will write 5 5's, I understand that and I think i understand why it is happening. I know the solution is just to do for (int i = 0; i < 5; i++) { int localI = i; Task.Factory.StartNew(() => Console.WriteLine(localI)); } Console.ReadLine(); However is something like this ok to do? Task currentTask = myFirstTask; currentTask.Start(); foreach (Task task in _TaskList) { currentTask.ContinueWith((antecendent) => { if(antecendent.IsCompleated) { task.Start(); } else //do error handling; }); currentTask = task; } } or do i need to do this? Task currentTask = myFirstTask; foreach (Task task in _TaskList) { Task localTask = task; currentTask.ContinueWith((antecendent) => { if(antecendent.IsCompleated) { localTask.Start(); } else //do error handling; }); currentTask = task; }

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• group by country with ActiveRecords in Rails

  - by Adnan

  Hello, I have a table with users: name | country | .. | UK | .. | US | .. | US | .. | UK | .. | FR | .. | FR | .. | UK | .. | UK | .. | DE | .. | DE | .. | UK | .. | CA | . . What is the most efficient way with ActiveRecords to get the list of countries in my view and for each country how many users are from, so: US 123 UK 54 DE 33 . . .

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