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• General advice and guidelines on how to properly override object.GetHashCode()

  - by Svish

  According to MSDN, a hash function must have the following properties: If two objects compare as equal, the GetHashCode method for each object must return the same value. However, if two objects do not compare as equal, the GetHashCode methods for the two object do not have to return different values. The GetHashCode method for an object must consistently return the same hash code as long as there is no modification to the object state that determines the return value of the object's Equals method. Note that this is true only for the current execution of an application, and that a different hash code can be returned if the application is run again. For the best performance, a hash function must generate a random distribution for all input. I keep finding myself in the following scenario: I have created a class, implemented IEquatable<T> and overridden object.Equals(object). MSDN states that: Types that override Equals must also override GetHashCode ; otherwise, Hashtable might not work correctly. And then it usually stops up a bit for me. Because, how do you properly override object.GetHashCode()? Never really know where to start, and it seems to be a lot of pitfalls. Here at StackOverflow, there are quite a few questions related to GetHashCode overriding, but most of them seems to be on quite particular cases and specific issues. So, therefore I would like to get a good compilation here. An overview with general advice and guidelines. What to do, what not to do, common pitfalls, where to start, etc. I would like it to be especially directed at C#, but I would think it will work kind of the same way for other .NET languages as well(?). I think maybe the best way is to create one answer per topic with a quick and short answer first (close to one-liner if at all possible), then maybe some more information and end with related questions, discussions, blog posts, etc., if there are any. I can then create one post as the accepted answer (to get it on top) with just a "table of contents". Try to keep it short and concise. And don't just link to other questions and blog posts. Try to take the essence of them and then rather link to source (especially since the source could disappear. Also, please try to edit and improve answers instead of created lots of very similar ones. I am not a very good technical writer, but I will at least try to format answers so they look alike, create the table of contents, etc. I will also try to search up some of the related questions here at SO that answers parts of these and maybe pull out the essence of the ones I can manage. But since I am not very stable on this topic, I will try to stay away for the most part :p

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• Catching OutOfMemoryError

  - by dotsid

  Documentation for java.lang.Error says: An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch But as java.lang.Error is subclass of java.lang.Throwable I can catch this type of throwable. I understand why this is not good idea to catch this sort of exceptions. As far as I understand, if we decide to caught it, the catch handler should not allocate any memory by itself. Otherwise OutOfMemoryError will be thrown again. So, my question is: is there any real word scenarios when catching java.lang.OutOfMemoryError may be a good idea? if we catching java.lang.OutOfMemoryError how can we sure that catch handler doesn't allocate any memory by itself (any tools or best practicies)? Thanks a lot.

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• What is better: CSS hacks or browser detection?

  - by Darryl Hein

  Commonly when I look around the Internet, I find that people are generally using CSS hacks to make their website look the same in all browsers. Personally, I have found this to be quite time consuming to find all of these hacks and test them; each change you make you have to test in 4+ browsers to make sure it didn't break anything else. About a year ago, I looked around the Internet for what other major sites are using (Yahoo, Google, BBC, etc) and found that most of them are doing some form of browser detection (JS, HTML if statements, server based). I have started doing this as well. On almost all of the sites I have worked on recently, I use jQuery, so I use the built in browser detection. Is there a reason you use or don't use either of these?

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• Assert a good practice or not ?

  - by rkenshin

  Is it a good practice to use Assert for function parameters to enforce their validity. I was going through the source code of Spring Framework and I noticed that they use Assert.notNull a lot. Here's an example public static ParsedSql parseSqlStatement(String sql) { Assert.notNull(sql, "SQL must not be null");} Here's Another one public NamedParameterJdbcTemplate(DataSource dataSource) { Assert.notNull(dataSource, "The [dataSource] argument cannot be null."); this .classicJdbcTemplate = new JdbcTemplate(dataSource); } public NamedParameterJdbcTemplate(JdbcOperations classicJdbcTemplate) { Assert.notNull(classicJdbcTemplate, "JdbcTemplate must not be null"); this .classicJdbcTemplate = classicJdbcTemplate; } Thank you

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• Cast then check or check then cast?

  - by jamesrom

  Which method is regarded as best practice? Cast first? public string Describe(ICola cola) { var coke = cola as CocaCola; if (coke != null) { string result; // some unique coca-cola only code here. return result; } var pepsi = cola as Pepsi; if (pepsi != null) { string result; // some unique pepsi only code here. return result; } } Or should I check first, cast later? public string Describe(ICola cola) { if (cola is CocaCola) { coke = (CocaCola) cola; string result; // some unique coca-cola only code here. return result; } if (cola is Pepsi) { pepsi = (Pepsi) cola; string result; // some unique pepsi only code here. return result; } } Can you see any other way to do this?

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• Why should i depend on a tool for my code review?

  - by Pandiya Chendur

  I have done with my web application. Now I am into code review phase. I have looked for some tools for code review in StackOverflow. But my question is: Why should I depend on a tool for my code review?

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• Organising asp.net website development process

  - by ZX12R

  Is there a standard practice to organize the process of developing a simple website. there is no use implementing MVC as there is no data base involved. It will be very useful in organizing the project and separating the aspx files and master page content(this can be very useful in implementing simple cms techniques) user controls scripts styles images is there any industry standard or best practice for this.? thanks in advance :) Update: yes the way i have listed is convenient. but it would be great if i could separate server codes and files like master,aspx.. and the actual page content. One more reason for not using MVC: I usually outsource the SEO process. Now an MVC application can be greek/latin for my SEO expert. :)

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• Etiquette for refactoring other people's sourcecode?

  - by Prutswonder

  Our team of software developers consists of a bunch of experienced programmers with a variety of programming styles and preferences. We do not have standards for everything, just the bare necessities to prevent total chaos. Recently, I bumped into some refactoring done by a colleague. My code looked somewhat like this: public Person CreateNewPerson(string firstName, string lastName) { var person = new Person() { FirstName = firstName, LastName = lastName }; return person; } Which was refactored to this: public Person CreateNewPerson (string firstName, string lastName) { Person person = new Person (); person.FirstName = firstName; person.LastName = lastName; return person; } Just because my colleague needed to update some other method in one of the classes I wrote, he also "refactored" the method above. For the record, he's one of those developers that despises syntactic sugar and uses a different bracket placement/identation scheme than the rest of us. My question is: What is the (C#) programmer's etiquette for refactoring other people's sourcecode (both semantic and syntactic)?

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• Fix common library functions, or abandon then?

  - by Ian Boyd

  Imagine i have a function with a bug in it: Boolean MakeLocation(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" return City+", "+State; } So the call: MakeLocation("Springfield", "MO"); would return "Springfield, MO" Now there's a slight problem, what if the user called: MakeLocation("Springfield, MO", "OH"); The called it wrong, obviously. But the function would return "Springfield, MO, OH". The system was functioning like this for many years, until i noticed the function being used wrong, and i corrected it. And i also updated the original function to catch such an obvious mistake - in case it's happening elsewhere: Boolean MakeLocation(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" if (City.Contains, ",") throw new EMakeLocationException("City name contains a comma. You probably didn't mean that"); return City+", "+State; } And testing showed the problem fixed. Except we missed an edge case, and the customer found it. So now the moral dillema. Do you ever add new sanity checks, safety checks, assertions to exising code? Or do you call the old function abandoned, and have a new one: Boolean MakeLocation(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" return City+", "+State; } Boolean MakeLocation2(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" if (City.Contains, ",") throw new EMakeLocationException("City name contains a comma. You probably didn't mean that"); return City+", "+State; } The same can apply for anything: Question FetchQuestion(Int id) { if (id == 0) throw new EFetchQuestionException("No question ID specified"); ... } Do you risk breaking existing code, at the expense of existing code being wrong?

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• Best Practise for Writing a POS System

  - by Gary

  Hi, I'm putting together a basic POS system in C# that needs to print to a receipt printer and open a cash drawer. Do I have to use the Microsoft Point of Service SDK? I've been playing around with printing to my Samsung printer using the Windows driver that came with it, and it seems to work great. I assume though that other printers may not come with Windows drivers and then I would be stuck? Or would I be able to simply use the Generic/Text Driver to print to any printer that supports it? For the cash drawer I would need to send codes directly to the COM port which is fine with me, if it saves me the hassle of helping clients setup OPOS drivers on there systems. Am I going down the wrong path here? Thanks, Gary

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• When to use custom exceptions vs. existing exceptions vs. generic exceptions

  - by Ryan Elkins

  I'm trying to figure out what the correct form of exceptions to throw would be for a library I am writing. One example of what I need to handle is logging a user in to a station. They do this by scanning a badge. Possible things that could go wrong include: Their badge is deactivated They don't have permission to work at this station The badge scanned does not exist in the system They are already logged in to another station elsewhere The database is down Internal DB error (happens sometimes if the badge didn't get set up correctly) An application using this library will have to handle these exceptions one way or another. It's possible they may decide to just say "Error" or they may want to give the user more useful information. What's the best practice in this situation? Create a custom exception for each possibility? Use existing exceptions? Use Exception and pass in the reason (throw new Exception("Badge is deactivated.");)? I'm thinking it's some sort of mix of the first two, using existing exceptions where applicable, and creating new ones where needed (and grouping exceptions where it makes sense).

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• Migrating from CPython to Jython

  - by itsadok

  I'm considering moving my code (around 30K LOC) from CPython to Jython, so that I could have better integration with my java code. Is there a checklist or a guide I should look at, to help my with the migration? Does anyone have experience with doing something similar? From reading the Jython site, most of the problems seem too obscure to bother me. I did notice that: thread safety is an issue Unicode support seems to be quite different, which may be a problem for me mysqldb doesn't work and needs to be replaced with zxJDBC Anything else? Related question: What are some strategies to write python code that works in CPython, Jython and IronPython

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• Do MSDTC and disaster recovery go together?

  - by DevDelivery

  Our application writes to multiple Sql Server databases within a distributed transaction. The Ops guys are saying that this messes up their disaster recovery plan because while the transactions on the live tables may commit at the same time, the log shipping on the separate databases happen at slightly different times. So in in a disaster recovery situation, there will be a few partial transactions. Is there a method for maintaining separate but synced databases in DR? Or do we have to re-design to relatively independent databases (or a single database)?

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• Building a Drupal Newsletter Module for handling Newsletter Articles

  - by Michael T. Smith

  We're building a module for generating HTML for email newsletters. We've looked into using a few other modules (SimpleNews, MailChimp, among others), but due to various requirements, it'll be easier and better for us to build a custom solution. Being a new Drupal developer, I'm a bit worried about handling this in a "non-Drupal" way. That being said, my plan is to setup a vocabulary with Newsletters as a term and the actual Newsletters as sub-terms, like so: Newsletters (term) - Newsletter A (sub-term) - Newsletter B (sub-term) This has the added benefit of being able to organize where articles were published (besides just on the site.) The question, though, is how to handle the different Newsletter issues. I could go another level deeper in the vocabulary, like so: Newsletters (term) - Newsletter A (sub-term) - Issue - 2010-03-01 - Issue - 2010-03-02 - Newsletter B (sub-term) - Issue - 2010-03-01 - Issue - 2010-03-08 But I'm wondering if this is adding a bit too much complexity. Once I have this taxonomy setup, when the user went to add new newsletters it would also create a node (content type: newsletter), and when he/she went to add new issues, it would also create a node (content type: issue.) Those would then be the landing pages for that content. So, the question is is there a better way for handling this structure? Is this a Drupal-like solution?

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• Perl unpack in list context

  - by drewk

  A common 'Perlism' is generating a list as something to loop over in this form: for($str=~/./g) { print "the next character from \"$str\"=$_\n"; } In this case the global match regex returns a list that is one character in turn from the string $str, and assigns that value to $_ Instead of a regex, split can be used in the same way or 'a'..'z', map, etc. I am investigating unpack to generate a field by field interpretation of a string. I have always found unpack to be less straightforward to the way my brain works, and I have never really dug that deeply into it. As a simple case, I want to generate a list that is one character in each element from a string using unpack (yes -- I know I can do it with split(//,$str) and /./g but I really want to see if unpack can be used this way...) Obviously, I can use a field list for unpack that is unpack("A1" x length($str), $str) but is there some other way that kinda looks like globbing? ie, can I call unpack(some_format,$str) either in list context or in a loop such that unpack will return the next group of character in the format group until $str is exausted? I have read The Perl 5.12 Pack pod and the Perl 5.12 pack tutorial and the Perkmonks tutorial Here is the sample code: #!/usr/bin/perl use warnings; use strict; my $str=join('',('a'..'z', 'A'..'Z')); #the alphabet... $str=~s/(.{1,3})/$1 /g; #...in groups of three print "str=$str\n\n"; for ($str=~/./g) { print "regex: = $_\n"; } for(split(//,$str)) { print "split: \$_=$_\n"; } for(unpack("A1" x length($str), $str)) { print "unpack: \$_=$_\n"; }

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• Simple ASP.Net MVC 1.0 Validation

  - by Mike

  On the current project we are working on we haven't upgraded to MVC 2.0 yet so I'm working on implementing some simple validation with the tools available in 1.0. I'm looking for feedback on the way I'm doing this. I have a model that represents a user profile. Inside that model I have a method that will validate all the fields and such. What I want to do is pass a controller to the validation method so that the model can set the model validation property in the controller. The goal is to get the validation from the controller into the model. Here is a quick example public FooController : Controller { public ActionResult Edit(User user) { user.ValidateModel(this); if (ModelState.IsValid) ....... ....... } } And my model validation signature is like public void ValidateModel(Controller currentState) What issues can you see with this? Am I way out to lunch on how I want to do this?

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• How can I effectively test a scripting engine?

  - by ChaosPandion

  I have been working on an ECMAScript implementation and I am currently working on polishing up the project. As a part of this, I have been writing tests like the following: [TestMethod] public void ArrayReduceTest() { var engine = new Engine(); var request = new ExecScriptRequest(@" var a = [1, 2, 3, 4, 5]; a.reduce(function(p, c, i, o) { return p + c; }); "); var response = (ExecScriptResponse)engine.PostWithReply(request); Assert.AreEqual((double)response.Data, 15D); } The problem is that there are so many points of failure in this test and similar tests that it almost doesn't seem worth it. It almost seems like my effort would be better spent reducing coupling between modules. To write a true unit test I would have to assume something like this: [TestMethod] public void CommentTest() { const string toParse = "/*First Line\r\nSecond Line*/"; var analyzer = new LexicalAnalyzer(toParse); { Assert.IsInstanceOfType(analyzer.Next(), typeof(MultiLineComment)); Assert.AreEqual(analyzer.Current.Value, "First Line\r\nSecond Line"); } } Doing this would require me to write thousands of tests which once again does not seem worth it.

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• Build and render infinite hierarchical category tree from self-referential category table

  - by FreshCode

  I have a Categories table in which each category has a ParentId that can refer to any other category's CategoryId that I want to display as multi-level HTML list, like so: <ul class="tree"> <li>Parent Category <ul> <li>1st Child Category <!-- more sub-categories --> </li> <li>2nd Child Category <!-- more sub-categories --> </li> </ul> </li> </ul> Presently I am recursively rendering a partial view and passing down the next category. It works great, but it's wrong because I'm executing queries in a view. How can I render the list into a tree object and cache it for quick display every time I need a list of all hierarchical categories?

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• Large svn external

  - by MPelletier

  I have a project which uses a large library residing in its own repository. Using: Tortoise-SVN, the server is running an enterprise edition of VisualSVN The project itself has the "standard" structure: trunk tags branches In each branch, tag, and trunk is the library, set as an external (svn:external property). If I get the entire tree, I get the library several times, which is just getting too ridiculously repetitive. Is there a recommended structure for this? Or perhaps a way not to get all externals (because other externals are much smaller, easier to manipulate)?

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• Java Builder pattern with Generic type bounds

  - by I82Much

  Hi all, I'm attempting to create a class with many parameters, using a Builder pattern rather than telescoping constructors. I'm doing this in the way described by Joshua Bloch's Effective Java, having private constructor on the enclosing class, and a public static Builder class. The Builder class ensures the object is in a consistent state before calling build(), at which point it delegates the construction of the enclosing object to the private constructor. Thus public class Foo { // Many variables private Foo(Builder b) { // Use all of b's variables to initialize self } public static final class Builder { public Builder(/* required variables */) { } public Builder var1(Var var) { // set it return this; } public Foo build() { return new Foo(this); } } } I then want to add type bounds to some of the variables, and thus need to parametrize the class definition. I want the bounds of the Foo class to be the same as that of the Builder class. public class Foo<Q extends Quantity> { private final Unit<Q> units; // Many variables private Foo(Builder<Q> b) { // Use all of b's variables to initialize self } public static final class Builder<Q extends Quantity> { private Unit<Q> units; public Builder(/* required variables */) { } public Builder units(Unit<Q> units) { this.units = units; return this; } public Foo build() { return new Foo<Q>(this); } } } This compiles fine, but the compiler is allowing me to do things I feel should be compiler errors. E.g. public static final Foo.Builder<Acceleration> x_Body_AccelField = new Foo.Builder<Acceleration>() .units(SI.METER) .build(); Here the units argument is not Unit<Acceleration> but Unit<Length>, but it is still accepted by the compiler. What am I doing wrong here? I want to ensure at compile time that the unit types match up correctly.

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• Constructor overloading in Java - best practice

  - by errr

  There are a few topics similar to this, but I couldn't find one with a sufficient answer. I would like to know what is the best practice for constructor overloading in Java. I already have my own thoughts on the subject, but I'd like to hear more advice. I'm referring to both constructor overloading in a simple class and constructor overloading while inheriting an already overloaded class (meaning the base class has overloaded constructors). Thanks :)

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• Why use Python interactive mode?

  - by mvid

  When I first started reading about Python, all of the tutorials have you use Python's Interactive Mode. It is difficult to save, write long programs, or edit your existing lines (for me at least). It seems like a far more difficult way of writing Python code than opening up a code.py file and running the interpreter on that file. python code.py I am coming from a Java background, so I have ingrained expectations of writing and compiling files for programs. I also know that a feature would not be so prominent in Python documentation if it were not somehow useful. So what am I missing?

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• POJO's versus Cursors in Android

  - by Kilnr

  I usually tend to define the model layer of my apps using POJO's, such as Article, Comment, etc. I was about to implement an AlphabetIndexer in the adapter of one of my ListViews. Right now this adapter accepts a Collection of Articles, which I normally get from my wrapper around an SQLiteDatabase. The signature of the AlphabetIndexer constructer is as follows: public AlphabetIndexer (Cursor cursor, int sortedColumnIndex, CharSequence alphabet) Since this doesn't accept a Collection or something similar, just a Cursor, it got me wondering: maybe I shouldn't be creating objects for my model, and just use the Cursors returned from the database? So the question is, I guess: what should I do, represent data with Collections of POJO's, or just work with Cursors throughout my app? Any input?

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• StringLengthValidator - localization not working

  - by danysdragons

  I am validating input to my ASP.NET application using StringLengthValidators, and using the ValidationSummary control to display the error messages. To localize the application, the StringLengthValidators have the MessageTemplateResourceName and MessageTemplateResourceType attributes set. The first time the validator runs, it picks up the correct error message based on the current culture setting. If I change the language setting while running the app, the next time the validator runs, the ValidationSummary it still displays the error message for the old culture. The text for all other controls is being updated correctly. Any ideas, folks?

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• WCF Timeout issue - should there even be a socket connection?

  - by stiank81

  I have a .Net application which is split into a client and server side. The communication between them is handled using WCF. I'm not using the automagic service references, but instead I've built the connection manually like described in the Screencast by Miguel Castro. Summarized this means that I create a console application on the server side that holds ServiceHost objects for the different services: var myServiceHost = new System.ServiceModel.ServiceHost(typeof(MyService), new Uri("net.tcp://localhost:8002")); myServiceHost.Open(); And on the client side I have service proxies creating channels using the ChannelFactory: IMyService proxy = new ChannelFactory<IMyService>("MyServiceEndpoint").CreateChannel(); The client and server side share the service contract defined in the interface IMyService. And another advantage is that I get minimal App.config files - without all the autogenerated stuff created through the Service References. Example from client side: <?xml version="1.0"?> <configuration> <system.serviceModel> <client> <endpoint address="net.tcp://localhost:8002/MyEndpoint" binding="netTcpBinding" contract="IMyService" name="MyServiceEndpoint"/> </client> </system.serviceModel> </configuration> So - to my problem. I create the proxy once, and it holds a channel all the way through the application. However, if I leave the application without use for a few minutes the channel has timed out, and I get the following exception: The socket connection was aborted. This could be caused by an error processing your message or a receive timeout being exceeded by the remote host, or an underlying network resource issue. Local socket timeout was '00:00:59.9979998'. How do I prevent this? I'm assuming I need to specify a higher timeout in my configuration? But I don't want it to ever time out. But on the other hand - I don't want a socket connection! Do I need one? Thought I could go connection less with WCF... What's the permanent solution and best practice on solving this? Set timeout to "never".. Create a new channel for each request? I'm assuming there is some overhead creating the channel?.. Increase the timeout to e.g. 5minutes and create new channel if the connection did timeout? Make it connection less somehow? (Without the overhead of creating channels..) Something else...

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