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• Why use I-prefix for interfaces in Java?

  - by Lars Andren

  Is there some reason why people use I-prefix for interfaces in Java? It seems to be a C#-convention spilling over. For C# it makes sense, as the answers to this question explains. However, for Java a class declaration clearly states which class that is extended and which interfaces that are implemented: public class Crow extends Animal implements Bird I think Joshua Bloch didn't suggest this in Effective Java, and I think he usually makes a lot of sense. I get the I-verbing as presented in an answer to the question above, but is there some other use with this convention for Java?

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• Why use multiple OpenGL context

  - by Luca

  For rendering I have a current GL context, associated to a window. In the case the application render multiple scenes (for example using accumulation or different viewports) I think it is ok to reuse the same context. My question, indeed, is: why should I use multiple GL context? I red on ARB_framebuffer_object extension spec that MakeCurrent call could be expansive, and in the case the ARB_framebuffer_object extension is present I can render on a generic buffer without using MakeCurrent. Apparently the only reason to use multiple GL context is to avoid to setup context state (pixel store, transfer, point size, polygon stipple...) or to have avaialable multiple render buffers configuration (one context with accumulation, another without). How to determine when is better an alternative context instead of setting context state? Thankyou all!

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• Why scala not allowing '$' identifier in case statement?

  - by Alex R

  this works as expected scala 3 match { case x:Int = 2*x } res1: Int = 6 why does this fail? scala 3 match { case $x:Int = 2*$x } :1: error: '=' expected but ':' found. 3 match { case $x:Int = 2*$x } ^ scala 3 match { case `$x`:Int = 2*$x } :1: error: '=' expected but ':' found. 3 match { case `$x`:Int = 2*$x } ^ scala 3 match { case `$x` : Int = 2*$x } :1: error: '=' expected but ':' found. 3 match { case `$x` : Int = 2*$x } '$' is supposed to be a valid identifier character, as demonstrated here: scala var y = 1 y: Int = 1 scala var $y = 2 $y: Int = 2 Thanks

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• CSharpCodeProvider: Why is a result of compilation out of context when debugging

  - by epitka

  I have following code snippet that i use to compile class at the run time. //now compile the runner var codeProvider = new CSharpCodeProvider( new Dictionary<string, string>() { { "CompilerVersion", "v3.5" } }); string[] references = new string[] { "System.dll", "System.Core.dll", "System.Core.dll" }; CompilerParameters parameters = new CompilerParameters(); parameters.ReferencedAssemblies.AddRange(references); parameters.OutputAssembly = "CGRunner"; parameters.GenerateInMemory = true; parameters.TreatWarningsAsErrors = true; CompilerResults result = codeProvider.CompileAssemblyFromSource(parameters, template); Whenever I step through the code to debug the unit test, and I try to see what is the value of "result" I get an error that name "result" does not exist in current context. Why?

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• Why would you want a case sensitive database?

  - by Khorkrak

  What are some reasons for choosing a case sensitive collation over a case insensitive one? I can see perhaps a modest performance gain for the DB engine in doing string comparisons. Is that it? If your data is set to all lower or uppercase then case sensitive could be reasonable but it's a disaster if you store mixed case data and then try to query it. You have then apply a lower() function on the column so that it'll match the corresponding lower case string literal. This prevents index usage in every dbms. So wondering why anyone would use such an option.

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• Why doesn't this Perl array sort work?

  - by Luke

  Why won't the array sort? CODE my @data = ('PJ RER Apts to Share|PROVIDENCE', 'PJ RER Apts to Share|JOHNSTON', 'PJ RER Apts to Share|JOHNSTON', 'PJ RER Apts to Share|JOHNSTON', 'PJ RER Condo|WEST WARWICK', 'PJ RER Condo|WARWICK'); foreach my $line (@data) { $count = @data; chomp($line); @fields = split(/\|/,$line); if ($fields[0] eq "PJ RER Apts to Share"){ @city = "\u\L$fields[1]"; @city_sort = sort (@city); print "@city_sort","\n"; } } print "$count","\n"; OUTPUT Providence Johnston Johnston Johnston 6

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• GDB hardware watchpoint very slow - why?

  - by Laurynas Biveinis

  On a large C application, I have set a hardware watchpoint on a memory address as follows: (gdb) watch *((int*)0x12F5D58) Hardware watchpoint 3: *((int*)0x12F5D58) As you can see, it's a hardware watchpoint, not software, which would explain the slowness. Now the application running time under debugger has changed from less than ten seconds to one hour and counting. The watchpoint has triggered three times so far, the first time after 15 minutes when the memory page containing the address was made readable by sbrk. Surely during those 15 minutes the watchpoint should have been efficient since the memory page was inaccessible? And that still does not explain, why it's so slow afterwards. The GDB is $ gdb --version GNU gdb (GDB) 7.0-ubuntu [...] Thanks in advance for any ideas as what might be the cause or how to fix/work around it.

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• Why does running rake gems:unpack result in a Gem::FilePermissionError

  - by Globalkeith

  I'm attempting to upgrade the friendly_id gem in a rails project. I have removed the old gem from the vendor directory, installed the new gem from rubygems.org. When I type: rake gems:unpack I get the following response: ERROR: While executing gem ... (Gem::FilePermissionError) You don't have write permissions into the /usr/lib/ruby/gems/1.8 directory. Sure, I realise I can sudo it, but what I don't understand is if I would like to unpack the gem into my project vender directory, why does it need access to /usr/lib/ruby/gems....

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• Why protected superclass member cannot be accessed in a subclass function when passed as an argument

  - by KNoodles

  I get a compile error, which I'm slightly confused about. This is on VS2003. error C2248: 'A::y' : cannot access protected member declared in class 'A' class A { public: A() : x(0), y(0) {} protected: int x; int y; }; class B : public A { public: B() : A(), z(0) {} B(const A& item) : A(), z(1) { x = item.y;} private: int z; }; The problem is with x = item.y; The access is specified as protected. Why doesn't the constructor of class B have access to A::y?

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• Why is SVN better than VSS? [closed]

  - by tsilb

  I've heard soooo many people complain about VSS, and noooo people complaining about SVN. We use SVN on my work project. It's slow, regularly freezes up my IDE, and has wonky behavior like looking for a database server every time I right-click the Solution node in my Solution Explorer. When I used VSS, everything worked beautifully, except for access restrictions which I of course blame on the people who control access. VSS is built by Microsoft and thus has great integration with Visual Studio. SVN is written by pretty much anybody with some free time (right?) and thus kinda works most of the time... And I honestly get the impression they had a dozen different directions in the design instead of one. So why do I keep hearing that SVN is better than VSS?

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• Why won't Silverlight handle the conversion of my custom float property

  - by Jeff Weber

  In a Silverlight 4 project I have a class that extends Canvas: public class AppendageCanvas : Canvas { public float Friction { get; set; } public float Restitution { get; set; } public float Density { get; set; } } I use this canvas in Blend by dragging it onto another control and setting the custom properties: When I run the app, I get the following error when InitializeComponent is called on the control containing my custom canvas: I'm not sure why Silverlight isn't able to convert this property from it's string representation in Xaml, to the float that it is. Anyone have any ideas?

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• Why is Yahoo Indexing Bot considered as "evil"?

  - by bigstylee

  After reading and commenting on this question PHP Library for Keeping your site index by Google, Bing, etc, I was curious to look at StackOverFlow's sitemap. This returned a 404 error which I am guessing is just a protected page by determining if your are a Index Bot or simply doesnt exists. This then lead me to look at the robots.txt for StackOverFlow. I was surprised to see the comment "Yahoo bot is evil" along with a couple other Indexing bots (Spinn3r and KSCrawler) . I am unfamilular with Spinn3r and KSCrawler but my question is, why are these bots (particular Yahoo) considered as evil? Surely any and all indexing of any Search Engine is a good thing?

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• Why dont Android applications provide an "Exit" option?

  - by Howiecamp

  Is there something in the Android developer guidelines that disuadea developers from providing the option to "exit" (stop running) an application from within the application itself? I love multitasking and all but it's not clear to me why: the vast majority of apps don't have their own Exit functions and hence just keep running forever don't give you a choice about running when you turn on the phone - they just do by default Both of these things lead to memory usage constantly increasing and your device running with this performance burden all of the time despite the fact that you may only want certain apps to run some of the time. Am I missing something?

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• Why is the base() constructor not necessary?

  - by Earlz

  Hello, I have a class structure like abstract class Animal { public Animal(){ //init stuff.. } } class Cat : Animal { public Cat(bool is_keyboard) : base() //NOTE here { //other init stuff } } Now then, look at the noted line. If you remove : base() then it will compile without an error. Why is this? Is there a way to disable this behavior? I have had multiple bugs now from forgetting the base() which I would have thought to be required on such a special thing as a constructor.

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• Actionscript: Why is drawRoundRectComplex() not documented?

  - by Chunk1978

  in studying actionscript 3's graphics class, i've come across the undocumented drawRoundRectComplex() method. it's a variant of drawRoundRect() but with 8 parameters, the final four being the diameter of each corner (x, y, width, height, top left, top right, bottom left, bottom right). //example var sp:Sprite = new Sprite(); sp.graphics.lineStyle(1, 0x000000); sp.graphics.drawRoundRectComplex(0, 0, 100, 50, 10, 20, 0, 10); addChild(sp); this seems to be a pretty useful method, so i'm just curious if anyone knows of any reasons why adobe chose not to document it?

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• State pattern: Why doesn't the context class implement or inherit the State abstract interface/class

  - by Ricket

  I'm reading about the State pattern. I have only just begun, so of course I begin by reading the entire Wikipedia article on it. I noticed that both of the examples in the article have some base abstract class or Java interface for a generic State's methods/functions. Then there are some states which inherit from the base and implement those methods/functions in different ways. Then there's a Context class which has a private member of type State and which, at any time, can be equal to an instance of one of the implementations. That context class also implements the same methods, and passes them onto the current state instance, and then has an additional method to change the state (or depending on design I understand the change of state could be a reaction to one of the implemented methods). Why doesn't this context class specifically "extend" or "implement" the generic State base class/interface?

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• Why wont this perl array sort work?

  - by Luke

  Why wont the array sort? CODE my @data = ('PJ RER Apts to Share|PROVIDENCE', 'PJ RER Apts to Share|JOHNSTON', 'PJ RER Apts to Share|JOHNSTON', 'PJ RER Apts to Share|JOHNSTON', 'PJ RER Condo|WEST WARWICK', 'PJ RER Condo|WARWICK'); foreach my $line (@data) { $count = @data; chomp($line); @fields = split(/\|/,$line); if ($fields[0] eq "PJ RER Apts to Share"){ @city = "\u\L$fields[1]"; @city_sort = sort (@city); print "@city_sort","\n"; } } print "$count","\n"; OUTPUT Providence Johnston Johnston Johnston 6

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• Why does GetClusterShape return null when the cluster specification was retrieved through the GetClu

  - by Markus Olsson

  Suppose I have a virtual earth shape layer called shapeLayer1 (my creative energy is apparently at an alltime low). When i call the GetClusteredShapes method I get an array of VEClusterSpecification objects that represent each and every one of my currently visible clusters; no problem there. But when I call the GetClusterShape() method it returns null... null! Why on earth would it do that? I used firebug to confirm that the private variable of the VEClusterSpecification that's supposed to hold a reference to the shape is indeed null so it's not the method that's causing the problem. Some have suggested that this is actually documented behavior Returns null if a VEClusterSpecification object was returned from the VEShapeLayer.GetClusteredShapes Method But looking at the current MSDN documentation for the VEShape class it says: Returns if a VEClusterSpecification object was returned from the VEShapeLayer.GetClusteredShapes Method Is this a bug or a feature? Is there any known workarounds or (if it is a bug) some plan on when they are going to fix it?

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• Why is scp not overwriting my destination file?

  - by Noli

  I'm trying to back up a file via the command scp /tmp/backup.tar.gz hostname:/home/user/backup.tar.gz When I run it, the scp progress bar shows up and it looks like its transferring the file, however when I log into the destination server to check the file, the timestamp and filesize haven't changed from the older version, so it looks like scp didn't overwrite the old file at all. It only sees to work when I manually delete the file from the destination server. I'm running ubuntu, and this is happening on two servers: one cygwin ssh, and one fedora core 3. Anyone have any idea why this is happening? I thought scp would ONLY overwrite existing files.. Thanks

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• Why are action based web frameworks predominant?

  - by deamon

  Most web frameworks are still using the traditional action based MVC model. A controller recieves the request, calls the model and delegates rendering to a template. That is what Rails, Grails, Struts, Spring MVC ... are doing. The other category, the component based frameworks like Wicket, Tapestry, JSF, or ASP.Net Web Forms have become more popular over the last years, but my perception is that the traditional action based approach is far more popular. And even ASP .Net Web Forms has become a sibling name ASP .Net Web MVC. I think the kind of applications built with both types of frameworks is overlapping very much, so the question is: Why are action based frameworks so predominant?

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• Why isn't Passenger respecting my custom log format?

  - by Millisami

  I need to change the log format of my rails app. I put this file in lib directory and required it in development.rb env file. require 'hodel_3000_compliant_logger' config.logger = Hodel3000CompliantLogger.new(config.log_path) and I should get the output of the development.log file as follows: Jun 28 03:05:13 millisami-notebook rails[18243]: Memory usage: 86888 | PID: 18243 I get this exact log when I start my app with script/server (Mongrel). But when I run the app via Passenger, the format being logged is Rails' default. Why doesn't Passenger write to the log file like Mongrel does?

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• Why doesn't this loop terminate?

  - by David

  Here's the sample code: public static void col (int n) { if (n % 2 == 0) n = n/2 ; if (n % 2 != 0) n = ((n*3)+1) ; System.out.println (n) ; if (n != 1) col (n) ; } this works just fine until it gets down to 2. then it outputs 2 4 2 4 2 4 2 4 2 4 infinitely. it seems to me that if 2 is entered as n then (n % 2 == 0) is true 2 will be divided by 2 to yeild 1. then 1 will be printed and since (n != 1) is false the loop will terminate. Why doesn't this happen?

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• Why is x86 ugly? aka Why is x86 considered inferior when compared to others?

  - by claws

  Hello, recently I've been reading some SO archives and encountered statements against x86 architecture. http://stackoverflow.com/questions/2667256/why-do-we-need-different-cpu-architecture-for-server-mini-mainframe-mixed-cor says "PC architecture is a mess, any OS developer would tell you that." http://stackoverflow.com/questions/82432/is-learning-assembly-language-worth-the-effort says "Realize that the x86 architecture is horrible at best" http://forums.anandtech.com/showthread.php?t=976577 says "Most colleges teach assembly on something like MIPS because it's much simpler to understand, x86 assembly is really ugly" and many more comments like Compared to most architectures, X86 sucks pretty badly. It's definitely the conventional wisdom that X86 is inferior to MIPS, SPARC, and PowerPC x86 is ugly I tried searching but didn't find any reasons. I don't find x86 bad probably because this is the only architecture I'm familiar with. Can someone kindly give me reasons for considering x86 ugly/bad/inferior compared to others.

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• Why better isolation level means better performance in SQL Server

  - by Oleg Zhylin

  When measuring performance on my query I came up with a dependency between isolation level and elapsed time that was surprising to me READUNCOMMITTED - 409024 READCOMMITTED - 368021 REPEATABLEREAD - 358019 SERIALIZABLE - 348019 Left column is table hint, and the right column is elapsed time in microseconds (sys.dm_exec_query_stats.total_elapsed_time). Why better isolation level gives better performance? This is a development machine and no concurrency whatsoever happens. I would expect READUNCOMMITTED to be the fasted due to less locking overhead. Update: I did measure this with DBCC DROPCLEANBUFFERS DBCC FREEPROCCACHE issued and Profiler confirms there're no cache hits happening. Update2: The query in question is an OLAP one and we need to run it as fast as possible. Closing the production server from outside world to get the computation done is not out of question if this gives performance benefits.

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• Why is this leaking memory? UIImage `cellForRowAtIndexPath:`

  - by Emil

  Hey. Instruments' Leaks tells me that this UIImage is leaking: UIImage *image = [[UIImage alloc] initWithContentsOfFile:[imagesPath stringByAppendingPathComponent:[NSString stringWithFormat:@"/%@.png", [postsArrayID objectAtIndex:indexPath.row]]]]; // If image contains anything, set cellImage to image. If image is empty, try one more time or use noImage.png, set in IB if (image != nil){ // If image != nil, set cellImage to that image cell.cellImage.image = image; } image = nil; [image release]; (class cell (custom table view cell) also releases cellImage in dealloc method). I haven't got a clue of why it's leaking, but it certainly is. The images gets loaded multiple times in a cellForRowAtIndexPath:-method. The first three cells' image does not leak (130px high, all the space avaliable). Leaks gives me no other info than that a UIImage allocated here in the code leaks. Can you help me figure it out? Thanks :)

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