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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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• Why timed lock doesnt throws a timeout exception in C++0x?

  - by Vicente Botet Escriba

  C++0x allows to lock on a mutex until a given time is reached, and return a boolean stating if the mutex has been locked or not. template <class Clock, class Duration> bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time); In some contexts, I consider an exceptional situation that the locking fails because of timeout. In this case an exception should be more appropriated. To make the difference a function lock_until could be used to get a timeout exception when the time is reached before locking. template <class Clock, class Duration> void lock_until(const chrono::time_point<Clock, Duration>& abs_time); Do you think that lock_until should be more adequate in some contexts? if yes, on which ones? If no, why try_lock_until will always be a better choice?

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• Why isn't the eigenclass equivalent to self.class, when it looks so similar?

  - by The Wicked Flea

  I've missed the memo somewhere, and I hope you'll explain this to me. Why is the eigenclass of an object different from self.class? class Foo def initialize(symbol) eigenclass = class << self self end eigenclass.class_eval do attr_accessor symbol end end end My train of logic that equates the eigenclass with class.self is rather simple: class << self is a way of declaring class methods, rather than instance methods. It's a shortcut to def Foo.bar. So within the reference to the class object, returning self should be identical to self.class. This is because class << self would set self to Foo.class for definition of class methods/attributes. Am I just confused? Or, is this a sneaky trick of Ruby meta-programming?

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• Haskell: Why is it saying my function type is off?

  - by linkmaster03

  I wrote a little Haskell program to find the area of a triangle, primarily to practice custom types, but it keeps throwing the following error on compile: areafinder.hs:7:4: Couldn't match expected type 'Triangle' against inferred type 'm b' In a stmt of a 'do' expression: putStr "Base: " In the expression: do { putStr "Base: "; baseStr I'm not sure where 'm b' comes from, so I'm at a loss here. Why is it throwing this error, and what can I do to fix it? Here is my code: module Main where data Triangle = Triangle Double Double -- base, height getTriangle :: Triangle getTriangle = do putStr "Base: " baseStr Double calcTriangle (Triangle base height) = base * height main = putStrLn ("Area = " ++ show (calcTriangle getTriangle)) Thanks. :)

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• Why the valid looking statement gives error in MATLAB?

  - by user198729

  It's from this question? Why the two solutions doesn't work, though it looks very valid for me: >> t = -pi:0.1:pi; >> r = ((sin(t)*sqrt(cos(t)))*(sin(t) + (7/5))^(-1)) - 2*sin(t) + 2 ; ??? Error using ==> mtimes Inner matrix dimensions must agree. >> t = -pi:0.1:pi; >> r = ((sin(t).*sqrt(cos(t))).*(sin(t) + (7/5)).^(-1)) - 2*sin(t) + 2 ; >> plot(r,t) ??? Error using ==> plot Vectors must be the same lengths. What's wrong with the above?

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• Why StringWriter.ToString return `System.Byte[]` and not the data?

  - by theateist

  UnZipFile method writes the data from inputStream to outputWriter. Why sr.ToString() returns System.Byte[] and not the data? using (var sr = new StringWriter()) { UnZipFile(response.GetResponseStream(), sr); var content = sr.ToString(); } public static void UnZipFile(Stream inputStream, TextWriter outputWriter) { using (var zipStream = new ZipInputStream(inputStream)) { ZipEntry currentEntry; if ((currentEntry = zipStream.GetNextEntry()) != null) { var size = 2048; var data = new byte[size]; while (true) { size = zipStream.Read(data, 0, size); if (size > 0) { outputWriter.Write(data); } else { break; } } } } }

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• Why does GetExportedValues<T>() no longer work after using the .net 4 final version of MEF?

  - by BigJason

  I have been developing a managed extensibility framework application for the last several months using the community preview. I have been using the GetExportedValues() method and the PartCreationPolicy(CreationPolicy.NonShared) to fake a class factory (since only the silverlight version supports a factory). This was working great until I upgraded the project to use .net 4.0. There is no error, it just doesn't work. So why did this code stop working? The code follows: The factory method: public static IEnumerable<DataActionBase> GetActionsFromDirectory(string PluginsFolder) { IEnumerable<DataActionBase> result = null; var catalog = new DirectoryCatalog(PluginsFolder); var container = new CompositionContainer(catalog: catalog); result = container.GetExportedValues<DataActionBase>(); return result; } Example Export Class: [Export(typeof(DataActionBase))] [PartCreationPolicy(CreationPolicy.NonShared)] public class AnAction : DataActionBase { .... }

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• Why am I not getting correct result when I calculate exponent with ^ in C++?

  - by xbonez

  I am using Bode's formuala to calculate distance of nth planet from sun dist = (4 + 3*(2^(n-2)))/10 If I calculate the distance this way, I get the right values: dist[2] = ((4 + 3*1)/10.0) ; dist[3] = ((4 + 3*2)/10.0) ; dist[4] = ((4 + 3*4)/10.0) ; But doing it this way, gives me incorrect values: vector <double> dist(5); for (unsigned int i = 2; i < 5; i++) { dist[i] = ((4 + 3*(2^(3-2)))/10.0) ; } Why so?

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• C: Why does gcc allow char array initialization with string literal larger than array?

  - by Ashwin

  int main() { char a[7] = "Network"; return 0; } A string literal in C is terminated internally with a nul character. So, the above code should give a compilation error since the actual length of the string literal Network is 8 and it cannot fit in a char[7] array. However, gcc (even with -Wall) on Ubuntu compiles this code without any error or warning. Why does gcc allow this and not flag it as compilation error? gcc only gives a warning (still no error!) when the char array size is smaller than the string literal. For example, it warns on: char a[6] = "Network"; [Related] Visual C++ 2012 gives a compilation error for char a[7]: 1>d:\main.cpp(3): error C2117: 'a' : array bounds overflow 1> d:\main.cpp(3) : see declaration of 'a'

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• Why do i get segfault at the end of the application after everything's beed done properly ?

  - by VaioIsBorn

  #include <string.h> #include <stdlib.h> #include <stdio.h> int main(void) { unsigned char *stole; unsigned char pass[] = "m4ak47"; printf("Vnesi password: \t"); scanf("%s", stole); if(strncmp(stole, pass, sizeof(pass)) != 0) { printf("wrong password!\n"); exit(0); } else printf("Password correct\n"); printf("some stuf here...\n\n"); return 0; } This program is working nice, but with one problem - if the password is correct then it DOES do the printing of 'some stuf here...' but it also shows me segmentation fault error at the end. Why ?

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• Why learn Perl, Python, Ruby if the company is using C++, C# or Java as the application language?

  - by szabgab

  I wonder why would a C++, C#, Java developer want to learn a dynamic language? Assuming the company won't switch its main development language from C++/C#/Java to a dynamic one what use is there for a dynamic language? What helper tasks can be done by the dynamic languages faster or better after only a few days of learning than with the static language that you have been using for several years? Update After seeing the first few responses it is clear that there two issues. My main interest would be something that is justifiable to the employer as an expense. That is, I am looking for justifications for the employer to finance the learning of a dynamic language. Aside from the obvious that the employee will have broader view, the employers are usually looking for some "real" benefit.

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• Can you tell me why my webpage displays differently in IE and how to fix it.

  - by b-rad

  I've been browsing through all of the CSS related cross-browser questions trying to troubleshoot my IE styling issues with no luck. Can anyone tell me how to fix my homepage styles so that it displays the same in IE as it currently does in Firefox? I've used Firebug (probably why it looks good in Firefox) but I can't find any tools for IE that will let me change the stylesheet real time. I'm just as interested in the process of figuring out this answer as I am in the answer itself so posting the steps you took to figure it out would be beneficial. (want to be able to do this myself next time!!!) Website is AppQandA.com. Scroll down to the bottom in IE and notice the footer. It's not like this on every page.....just the main page and the questions page.

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• Why do virtual memory addresses for linux binaries start at 0x8048000?

  - by muteW

  Disassembling an ELF binary on a Ubuntu x86 system I couldn't help but notice that the code(.text) section starts from the virtual address 0x8048000 and all lower memory addresses seem to be unused. This seems to be rather wasteful and all Google turns up is either folklore involving STACK_TOP or protection against null-pointer dereferences. The latter case looks like it can be fixed by using a single page instead of leaving a 128MB gap. So my question is this - is there a definitive answer to why the layout has been fixed to these values or is it just an arbitrary choice?

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• Why does the app signature change in Android after a classpath change?

  - by espinchi

  I have an Android project that branched into three different applications, app-1, app-2 and app-3, that apply some customizations. Currently there is a lot of code duplication, making maintenance a nightmare: do the changes in one of the branches, and then merge the other two. So we create a library project, named app-core, that factors out most of the duplicated code. So far so good. When I launch this into an emulator where the application was already loaded (before the refactoring), I get this exception: Re-installation failed due to different application signatures A different signature? But I just added a line in the .classpath to link to the app-core Java project! The main question is: are the existing users going to be bothered by this too? And the side question: Why is it a different signature?

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• Why can't I open a new window on my jquery ajax callback?

  - by KyleGobel

  to show my problem in a couple examples... THIS WORKS $.post("SomePage.aspx", { name : "value" }, function (data) { alert(data); }, "text"); THIS DOESN'T WORK $.post("SomePage.aspx", { name : "value" }, function (data) { window.open("http://www.google.com"); }, "text"); In the first example, I get alerted with what i'm expecting. In the second example, nothing happens. No window is opened. If I add an alert or something before or after the window.open call, the alert works fine, but the window doesn't open. If I add a window.open completly after the $.post method, the window opens fine (of course this doens't help me at all). I'm wondering why I can't open a window in the callback. What do I have to do to be able to open a window? I'd like to open a window to show some fancy results. Any help is appreciated, thanks.

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• Why is this javascript function so slow on Firefox?

  - by macrael

  This function was adapted from the website: http://eriwen.com/javascript/measure-ems-for-layout/ function getEmSize(el) { var tempDiv = document.createElement("div"); tempDiv.style.height = "1em"; el.appendChild(tempDiv); var emSize = tempDiv.offsetHeight; el.removeChild(tempDiv); return emSize; } I am running this function as part of another function on window.resize, and it is causing performance problems on Firefox 3.6 that do not exist on current Safari or Chrome. Firefox's profiler says I'm spending the most time in this function and I'm curious as to why that is. Is there a way to get the em size in javascript without doing all this work? I would like to recalculate the size on resize incase the user has changed it.

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• Why is selecting specified columns, and all, wrong in Oracle SQL?

  - by TomatoSandwich

  Say I have a select statement that goes.. select * from animals That gives a a query result of all the columns in the table. Now, if the 42nd column of the table animals is is_parent, and I want to return that in my results, just after gender, so I can see it more easily. But I also want all the other columns. select is_parent, * from animals This returns ORA-00936: missing expression. The same statement will work fine in Sybase, and I know that you need to add a table alias to the animals table to get it to work ( select is_parent, a.* from animals ani), but why must Oracle need a table alias to be able to work out the select?

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• Perl: Why does "use strict" not let me pass a parameter hash?

  - by Thariama

  I hava a perl subroutine where i would like to pass parameters as a hash (the aim is to include a css depending on the parameter 'iconsize'). I am using the call: get_function_bar_begin('iconsize' => '32'); for the subroutine get_function_bar_begin: use strict; ... sub get_function_bar_begin { my $self = shift; my %template_params = %{ shift || {} }; return $self->render_template('global/bars /tmpl_incl_function_bar_begin.html',%template_params); } Why does this yield the error message: Error executing run mode 'start': undef error - Can't use string ("iconsize") as a HASH ref while "strict refs" in use at CheckBar.pm at line 334 Am i doing something wrong here? Is there an other way to submit my data ('iconsize') as a hash?

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• Why is Rake not able to invoke multiple tasks consecutively?

  - by PandaWood

  I have a Rake task which I have simplified below. I'm using Ruby 1.9 on Windows. Perhaps you would like to guess the outcome of calling the Rake task "list_all_levels" below? It should be: "Hello level 1" "Hello level 2" "Hello level 3" But for reasons unknown to me, it prints only "Hello level 1" and then stops. That is, it always invokes only the first task. If I change the first line to pass the arg "42", it would print "Hello level 42" and then stop. I'm wondering why does it not invoke the task 3 times and print all 3 lines? And is there any way to get it to work how I would expect? task :list_all_levels => [] do Rake::Task[:list].invoke 1 Rake::Task[:list].invoke 2 Rake::Task[:list].invoke 3 end task :list, [:level] => [] do |t, args| puts "Hello level #{args.level}" end

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• Why am I getting a Java NoSuchPortException when the port exists?

  - by user258526

  Got the following production code below, I'm using it for a new driver. portName is COM4 and this port exists on the PC (and I can connect to it with hyperterminal), so why does Javacomm throw a NoSuchPortException? COM4 shows up fine in device mgr. too final String portName = getSerialPort(); try { final CommPortIdentifier id = CommPortIdentifier.getPortIdentifier(portName); port = (SerialPort) id.open(getName(), 1000); } catch (NoSuchPortException nspe) { report(SeverityCode.LEVEL2, getName(), "PIN Pad is not connected to " + portName + " port, or the port does not exist."); return; } catch (PortInUseException piue) { report(SeverityCode.LEVEL2, getName(), portName + " port is already in-use by some other device. Reason: " + piue.getMessage()); return; }

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• Why is using a Non-Random IV with CBC Mode a vulnerability?

  - by The Rook

  I understand the purpose of an IV. Specifically in CBC mode this insures that the first block of of 2 messages encrypted with the same key will never be identical. But why is it a vulnerability if the IV's are sequential? According to CWE-329 NON-Random IV's allow for the possibility of a dictionary attack. I know that in practice protocols like WEP make no effort to hide the IV. If the attacker has the IV and a cipher text message then this opens the door for a dictionary attack against the key. I don't see how a random iv changes this. (I know the attacks against wep are more complex than this.) What security advantage does a randomized iv have? Is this still a problem with an "Ideal Block Cipher"? (A perfectly secure block cipher with no possible weaknesses.)

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• When and why does an EventHandler require objects to be final?

  - by Michiel Borkent

  I have the following code from a GWT Project that is part of the onModuleLoad() method (similar to Java's main method, if you don't know GWT): final TextBox t1 = new TextBox(); final Label lt1 = new Label(); t1.addKeyUpHandler(new KeyUpHandler() { @Override public void onKeyUp(KeyUpEvent event) { // TODO Auto-generated method stub if (!(t1.getText().matches("\\w{2}-\\w{2}-\\w{2}"))) lt1.setText("Invalid."); else lt1.setText("OK."); } }); Why do the two local variables have to be final here?

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• Objective-C why doesn't my array of array works?

  - by Quetsche

  This is probably a completely stupid question, but i'm pretty new at objective-C and programing in general. i'm trying to make an array of arrays but can't manage to make it work : @interface ArraysAndDicts : NSObject { NSMutableArray * mySimpleArray; NSMutableArray * myComplicatedArray; } the implementation : -(void)generateValueForArrayOfArrays { [self generateValueForArray]; //this generates an array with 5 elements 'mySimpleArray' [myComplicatedArray addObject:mySimpleArray]; NSMutableArray * mySecondaryArray = [[NSMutableArray alloc] init]; [mySecondaryArray addObject:@"twoone"]; [mySecondaryArray addObject:@"twotwo"]; [myComplicatedArray addObject:mySecondaryArray]; (i edited out all the NSLogs for clarity) When running my app, the console tells me : mySecondaryArray count = 2 mySimpleArray count = 5 myComplicatedArraycount = 0 So, i know there are other ways to make multidimensional arrays, but i'd really like to know why this doesn't work. Thank you.

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• Why don't hardware failures show up at the programming language level?

  - by Julian Cienfuegos

  I am wondering if anyone can give my a good answer, or at least point me in the direction of a good reference to the following question: How come I have never heard of a computer breaking in a very fundamental way? How come when I declare x to be a double it stays as a double? How come there is never a short circuit that robs it of some bytes and makes it an integer? Why do we have faith that when we initialize x to 10, there will never be a power surge that will cause it to become 11, or something similar? I think I need a better understanding of memory. Thanks, and please don't bash me over the head for such a simple/abstract question.

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• why number 9 in kill -9 command in unix?

  - by Alby

  I understand it's off topic, I couldn't find anywhere online and I was thinking maybe programming gurus in the community might know this. I usually use kill -9 pid to kill the job. I always wondered the origin of 9. I looked it up online, and it says "9 Means KILL signal that is not catchable or ignorable. In other words it would signal process (some running application) to quit immediately" (source: http://wiki.answers.com/Q/What_does_kill_-9_do_in_unix_in_its_entirety) But, why 9? and what about the other numbers? is there any historical significance or because of the architecture of Unix? Thanks!

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