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  • can this keyword be used in an abstract class in java

    - by Reddy
    I tried with below example, it is working fine. I expected it to pick sub-class's value since object won't be created for super class (as it is abstract). But it is picking up super class's field value only. Please help me understand what is the concepts behind this? abstract class SuperAbstract { private int a=2; public void funA() { System.out.println("In SuperAbstract: this.a "+a); } } class SubClass extends SuperAbstract { private int a=34; } I am calling new SubClass.funA(); I am expecting it to print 34, but it is printing 2.

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  • can the keyword 'this' be used in an abstract class in java

    - by Reddy
    I tried with below example, it is working fine. I expected it to pick sub-class's value since object won't be created for super class (as it is abstract). But it is picking up super class's field value only. Please help me understand what is the concepts behind this? abstract class SuperAbstract { private int a=2; public void funA() { System.out.println("In SuperAbstract: this.a "+a); } } class SubClass extends SuperAbstract { private int a=34; } I am calling new SubClass.funA(); I am expecting it to print 34, but it is printing 2.

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  • Design pattern: Polymorphism for list of objects

    - by ziang
    Suppose I have a class A, and A1, A2 inherits from A. There are 2 functions: List<A1> getListA1(){...} List<A2> getListA2(){...} Now I want to do something similar to both A1 and A2 in another function public void process(List<A>){...} If I want to pass the instance of either ListA1 or ListA2, of course the types doesn't match because the compiler doesn't allow the coercion from List< A1 to List< A. I can't do something like this: List<A1> listA1 = getListA1(); List<A> newList = (List<A>)listA1; //this is not allowed. So what is the best approach to the process()? Is there any way to do it in a universal way rather than write the similar code to both List and List?

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  • When to use try/catch

    - by coffeeaddict
    I'm always finding myself wanting to put a try/catch around the lets say Business Layer methods. But I feel though that I don't need a try/catch if I'm simply rethrowing it up to the Presentation Layer. Is that right? I should not be rethrowing an exception from code that's wrapped in a try/catch in a BL method and should be letting the caller which would be from the Presentation Layer code be using a try/catch to handle it there? The BL method will throw an error without the try/catch anyway..the compiler will. So it wouldn't make sense to use a try/catch in a BL method that's to be consumed by a layer higher up correct?

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  • Setting enum values to 4-byte strings - why?

    - by psychotik
    I saw code similar to this in the Mac OS SDK: enum { kAudioFileStreamProperty_ReadyToProducePackets = 'redy', kAudioFileStreamProperty_FileFormat = 'ffmt', kAudioFileStreamProperty_DataFormat = 'dfmt', kAudioFileStreamProperty_FormatList = 'flst', kAudioFileStreamProperty_MagicCookieData = 'mgic', kAudioFileStreamProperty_AudioDataByteCount = 'bcnt', kAudioFileStreamProperty_AudioDataPacketCount = 'pcnt', kAudioFileStreamProperty_MaximumPacketSize = 'psze', kAudioFileStreamProperty_DataOffset = 'doff', kAudioFileStreamProperty_ChannelLayout = 'cmap', kAudioFileStreamProperty_PacketToFrame = 'pkfr', kAudioFileStreamProperty_FrameToPacket = 'frpk', kAudioFileStreamProperty_PacketToByte = 'pkby', kAudioFileStreamProperty_ByteToPacket = 'bypk', kAudioFileStreamProperty_PacketTableInfo = 'pnfo', kAudioFileStreamProperty_PacketSizeUpperBound = 'pkub', kAudioFileStreamProperty_AverageBytesPerPacket = 'abpp', kAudioFileStreamProperty_BitRate = 'brat' }; It's the first time I've seen this - I assume the compiler assigns the 32-bit integer equivalent of the strings to the enum values. I cannot think of a single good reason why this might be preferred over using simple integers. It looks hideous in a debugger (how do you tell which of these values corresponds to 1919247481?) and makes debugging just hard in general. So, is there any reason where assigning such strings to enum values actually makes sense.

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  • What is the Effect of Declaring 'extern "C"' in the Header to a C++ Shared Library?

    - by Adam
    Based on this question I understand the purpose of the construct in linking C libraries with C++ code. Now suppose the following: I have a '.so' shared library compiled with a C++ compiler. The header has a 'typedef stuct' and a number of function declarations. If the header includes the extern "C" declaration... #ifdef __cplusplus extern "C" { #endif // typedef struct ...; // function decls #ifdef __cplusplus } #endif ... what is the effect? Specifically I'm wondering if there are any detrimental side effects of that declaration since the shared library is compiled as C++, not C. Is there any reason to have the extern "C" declaration in this case?

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  • Is it possible to retrieve only a single property from a CSS class?

    - by werner5471
    Example CSS File: .testClass { color: black; background: red; } Now in an HTML file, I would like to have something like <span class="testClass:color">Text in black but without red background</span> to only apply the color property of that class. Is there a way to do this? The purpose behind it (for people asking themselves "Why the hell would he want that, that's not clean CSS usage!") is that I use jQuery UI themes, and I would like the entire page to fit a theme upon change. As not all kinds of elements (e.g. the color of a link) are covered by those themes, in those cases I would like to "steal" the color property (but not more) of some other CSS class of the jQuery UI theme. If there is another way to do this, of course I'm glad to hear it as well!

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  • Why does C++ allow variable length arrays that aren't dynamically allocated?

    - by Maulrus
    I'm relatively new to C++, and from the beginning it's been drilled into me that you can't do something like int x; cin >> x; int array[x]; Instead, you must use dynamic memory. However, I recently discovered that the above will compile (though I get a -pedantic warning saying it's forbidden by ISO C++). I know that it's obviously a bad idea to do it if it's not allowed by the standard, but I previously didn't even know this was possible. My question is, why does g++ allow variable length arrays that aren't dynamically allocated if it's not allowed by the standard? Also, if it's possible for the compiler to do it, why isn't it in the standard?

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  • What's the best way to debug AJAX to PHP calls?

    - by Jascha
    I'm having a miserable time debugging one small function on my new project. Essentially I'm having a user log out via an AJAX call to my log out script on my server called "userfFunctions.php" I'm using AJAX so that I don't have the headache of writing more regex to match my mod_rewrites. Anyway, every so often, it seems as though my Post data just flat out dies and since the PHP is running behind the scenes, I feel like I have no way of finding out where the data flow is being disrupted. BTW This function works 19 hrs of the day. Here is the javascript function: function logOut(){ var data = new Object; data.log_out = true; $.ajax({ type: 'POST', url: 'http://www.mydomain.com/User_Validator', //<-- redirects to userFunctions.php data: data, success: function(data) { alert(data); // <-- a response is triggered but with no response data! } }); } the php side: if(isset($_POST['log_out'])){ echo 'alert this!'; } here is my awesome response:

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  • Why is super.super.method(); not allowed in Java?

    - by Tim Büthe
    I read this question and thought that would easily be solved (not that it isn't solvable without) if one could write: @Override public String toString() { return super.super.toString(); } I'm not sure if it is useful in many cases, but I wonder why it isn't and if something like this exists in other languages. What do you guys think? EDIT: To clarify: yes I know, that's impossible to at to Java and I don't really miss it. This is nothing I expected to work and was surprised getting a compiler error. I just had the idea and like to discuss it.

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  • Can I use a static var to "cache" the result? C++

    - by flyout
    I am using a function that returns a char*, and right now I am getting the compiler warning "returning address of local variable or temporary", so I guess I will have to use a static var for the return, my question is can I make something like if(var already set) return var else do function and return var? This is my function: char * GetUID() { TCHAR buf[20]; StringCchPrintf(buf, 20*sizeof(char), TEXT("%s"), someFunction()); return buf; } And this is what I want to do: char * GetUID() { static TCHAR buf[20]; if(strlen(buf)!=0) return buf; StringCchPrintf(buf, 20*sizeof(char), TEXT("%s"), someFunction()); return buf; } Is this a well use of static vars? And should I use ZeroMemory(&buf, 20*sizeof(char))? I removed it because if I use it above the if(strlen...) my TCHAR length is never 0, should I use it below?

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  • How to reliably specialize template with intptr_t in 32 and 64 bit environments?

    - by vava
    I have a template I want to specialize with two int types, one of them plain old int and another one is intptr_t. On 64 bit platform they have different sizes and I can do that with ease but on 32 bit both types are the same and compiler throws an error about redefinition. What can I do to fix it except for disabling one of definitions off with preprocessor? Some code as an example: template<typename T> type * convert(); template<> type * convert<int>() { return getProperIntType(sizeof(int)); } template<> type * convert<intptr_t>() { return getProperIntType(sizeof(intptr_t)); } //this template can be specialized with non-integral types as well, // so I can't just use sizeof() as template parameter. template<> type * convert<void>() { return getProperVoidType(); }

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  • How can I get jquery .val() AFTER keypress event?

    - by werner5471
    I got: $(someTextInputField).keypress(function() { alert($(this).val()); }); Now the alert always returns the value BEFORE the keypress (e.g. the field is empty, I type 'a' and the alert gives me ''. Then I type 'b' and the alert gives me 'a'...). But I want the value AFTER the keypress - how can I do that? Background: I'd like to enable a button as soon as the text field contains at least one character. So I run this test on every keypress event, but using the returned val() the result is always one step behind. Using the change() event is not an option for me because then the button is disabled until you leave the text box. If there's a better way to do that, I'm glad to hear it!

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  • Display local image in iPhone HTML mail

    - by Sjakelien
    Hello there, In my app, I am composing an HMTL email message with the 3.0+ MFMailComposeViewController. To do this, I created an HTML file, with some placeholders. In my code, I read the HTML file, and with replaceOccurrencesOfString, I replace the placeholders with data from the app. In that way, I compose the body of the email I want to send out. This is all working very nicely, except for the fact, that in my HTML file, I have an <img src='imageplaceholderpath' /> tag. Somehow, I cannot figure out, with what I should replace this imageplaceholderpath, in order to refer to an image that resides in my app. Is this a valid approach at all, and if so, what would be the syntax/logic behind the path I should put there? I do appreciate your insights! Regards Sjakelien

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  • Contents changed(cleared?) when access the pointer returned by std::string::c_str()

    - by justamask
    string conf()     {         vector v;         //..         v = func(); //this function returns a vector         return v[1];     }     void test()     {         const char* p = conf().c_str();         // the string object will be alive as a auto var         // so the pointer should be valid till the end of this function,right?           // ... lots of steps, but none of them would access the pointer p         // when access p here, SOMETIMES the contents would change ... Why?         // the platform is solaris 64 bit         // compiler is sun workshop 12         // my code is compiled as  ELF 32-bit MSB relocatable SPARC32PLUS Version 1, V8+ Required         // but need to link with some shared lib which are ELF 32-bit MSB dynamic lib SPARC Version 1, dynamically linked, stripped     }

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  • Casting to specific asp.net page type

    - by DEH
    I have an asp.net page with a code-behind class definition as follows: public partial class examplepage : System.Web.UI.Page I'd like to set a public property within the page that I can reference from other classes. My understanding is that if I cast to examplepage then I should be able to get at the public property that is specific to example page, as in: string test=((examplepage)HttpContext.Current.Handler).propertyX; However, when I try casting as above the compiler does not recognise examplepage. Can anyone tell me how I can cast? I have no specific namespaces defined. Thanks

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  • Normalized Device Coordinates to window coordinates

    - by okoman
    I just read some stuff about the theory behind 3d graphics. As I understand it, normalized device coordinates (NDC) are coordinates that describe a point in the interval from -1 to 1 on both the horizontal and vertical axis. On the other hand window coordinates describe a point somewhere between (0,0) and (width,height) of the window. So my formula to convert a point from the NDC coordinate system to the window system would be xwin = width + xndc * 0.5 * width ywin = height + ynfv * 0.5 * height The problem now is that in the OpenGL documentation for glViewport there is an other formula: xwin = ( xndc + 1 ) * width * 0.5 + x ywin = ( yndc + 1 ) * height * 0.5 + y Now I'm wondering what I am getting wrong. Especially I'm wondering what the additional "x" and "y" mean. Hope the question isn't too "not programming related", but I thought somehow it is related to graphics programming.

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  • Eclipse RCP: How to troubleshoot plugin dependencies & classpath problems?

    - by paul
    I am working on an RCP project based on eclipse. It has been working fine but recently I thought I'd upgrade it to use a new eclipse version (3.2 - 3.5). After a bit of trouble, it seemed to be working fine. Then I did something. Don't know what. The end result is that I'm getting a classpath error when one of my plugins (A) tries to access a class in one of the dependent plugins (B) (also one of mine). As far as I can see, Plugin A has Plugin B in its' dependency list and the compiler shows no errors. To test, I created a new Plugin C with one class and accessed the class from Plugin A. That works fine. Does anyone have any hints for troubleshooting such issues? A checklist of settings to check? I've been stuggling with this for hours and getting nowhere! Particularly frustrating as it was working until I changed something! Thanks

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  • Positioning the dialog box in the centre of the screen

    - by ame
    I have a dialog box developed in mfc for a Windows CE device and want it to occupy the entire screen. I used the following code to center my dialog box on the lcd screen of the device: CWnd* pWnd = GetDesktopWindow(); CenterWindow(pWnd); However, I still get a tiny sliver of space on the left side of the dialog box, resizing the dialog merely makes it overflow on the right side of the LCD while the tiny space on the left remains (I can see the blue of the win CE desktop behind.) Are there any suggestions to solve this problem? I checked the margin settings for this dialog box in my .rc files and leftmargin and topmargin are both set to 0. I was wondering if I could get the coordinates of the centre of the screen and then place my window one or two points to the left to deal with the current offset. A messy approach I know!

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  • css position question: layers with z-index?

    - by user239831
    hey guys, i have a probably rather simpel problem: my website has two layers: 1) a drag&drop navigation on top which should be positioned absolute, so scrolling doesn't affect the bars. 2) a content area in the back behind the navigation which should be scrollable. you can see what i mean right here: http://jsfiddle.net/Pghqv/ however now, i cannot click links in my content-area in the back. any ideas or solutions how i can still have the same position result and the links in the back are working? thank you very much.

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  • Java import from other directory

    - by heldopslippers
    Hi People! I am building a Enterprise Service Bus (ESB) with Java. I won't get into details But I have to build multiple servers who make use of the same classes. I have the following directory structure: /server1 -Main.java /server2 -Main.java /com -Database.java I want to import from the Main.java class for example the Database.class. But of course the following statements won't work: import com.Database; I am working with the javac compiler in the command line (so not eclipse stuff or whatever. just TextMate and the command line). And I found a (pretty stupid) solution by creating a symbolic link in the servers to the com directory. But that is not really an ideal solution. Does anybody have a better one?? THANXS in advanced!! :D

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  • Static initialization of a struct with class members

    - by JS Bangs
    I have a struct that's defined with a large number of vanilla char* pointers, but also an object member. When I try to statically initialize such a struct, I get a compiler error. typedef struct { const char* pszA; // ... snip ... const char* pszZ; SomeObject obj; } example_struct; // I only want to assign the first few members, the rest should be default example_struct ex = { "a", "b" }; SomeObject has a public default constructor with no arguments, so I didn't think this would be a problem. But when I try to compile this (using VS), I get the following error: error C2248: 'SomeObject::SomeObject' : cannot access private member declared in class 'SomeObject' Any idea why?

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  • Indexing an image in-between already made content

    - by Christophersson
    I have a pre-code page coded as follows: <div id="linearBg"> <div id="wrapper"> <div class="logo"></div> <div class="navigation"></div> <div class="video"></div> <div class="content"></div> </div> </div> Where linearBg is a gradient background, the back board of the website. Wrapper is the container for the inner div's, and the rest are content oriented. So i've already implemented this with styles and all sorts, but the thing is I want to add: <div class="watermark"></div> underneath/behind both the content and video div, sort of like a reverse watermark, I've tried z-indexing but i'm not an expert. Could you guide me on to do make this possible? Thanks in advance

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  • Rscript does not recognize setGeneric function

    - by Branko K.
    I am trying to convert an R script into something that a client can run in batch mode. My code uses generic functions and one snippet which is near the beginning goes like: setGeneric("testInput", function(inputData, params = list()) standardGeneric("testInput")) I've been using R CMD BATCH and it works fine. However I couldn't find an easy way to make my script print the output on the console, so based on that (and suggestion that Rscript.exe is the "proper" way to run R batch files) I decided to switch to Rscript. However when running the very same .R file with Rscript I get the following: Error: could not find function "setGeneric" Execution halted I know there is probably a trivial reason behind this but I just cannot figure it out. Can someone please point me to where the mistake is? Thanks so much in advance. Cheers!

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  • Are there any well-known algorithms or computer models that computer scientists use to predict FIFA

    - by Khnle
    Occasionally I read news articles that mention about some computer models that computer scientists use to predict winners of some sporting events or the odds for betting which I think there must be a mathematical model behind it. I never bothered to think twice even though I am a "pseudo computer scientist" myself. With the 2010 FIFA World Cup just underway, and since I am also a "pseudo football/soccer player" myself, I just started to wonder about these calculations algorithms. For example, I know one factor is determining the strength of opponents, so that a win against a strong opponent can count more than a win against a weak opponent. But it now kind of gets in a circular loop, or at least how does one determine the strength of a team in the first place, before that team can be considered strong or weak? If it's based on a historical data then there's no way that could be accurate, because those players of the past are no longer on the fields so their impact is none (except maybe if they become coaches like Maradona) Anyway, long question short, if you're happen to be working in this field or have some knowledge, please shed some lights.

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