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  • Singletons and constants

    - by devoured elysium
    I am making a program which makes use of a couple of constants. At first, each time I needed to use a constant, I'd define it as //C# private static readonly int MyConstant = xxx; //Java private static final int MyConstant = xxx; in the class where I'd need it. After some time, I started to realise that some constants would be needed in more than one class. At this time, I had 3 choises: To define them in the different classes that needed it. This leads to repetition. If by some reason later I need to change one of them, I'd have to check in all classes to replace them everywhere. To define a static class/singleton with all the constants as public. If I needed a constant X in ClassA, ClassB and ClassC, I could just define it in ClassA as public, and then have ClassB and ClassC refer to them. This solution doesn't seem that good to me as it introduces even more dependencies as the classes already have between them. I ended up implementing my code with the second option. Is that the best alternative? I feel I am probably missing some other better alternative. What worries me about using the singleton here is that it is nowhere clear to a user of the class that this class is using the singleton. Maybe I could create a ConstantsClass that held all the constants needed and then I'd pass it in the constructor to the classes that'd need it? Thanks

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  • Encapsulating a Windows.Forms.Button

    - by devoured elysium
    I want to define a special kind of button that only allows two possible labels: "ON" and "OFF". I decided to inherit from a Windows.Forms.Button to implement this but now I don't know I how should enforce this rule. Should I just override the Text property like this? public override string Text { set { throw new InvalidOperationException("Invalid operation on StartStopButton!"); } } The problem I see with this is that I am breaking the contract that all buttons should have. If any code tries something like foreach (Button button in myForm) { button.Text = "123"; } they will get an Exception if I have any of my special buttons on the form, which is something that isn't expectable. First, because people think of properties just as "public" variables, not methods, second, because they are used to using and setting whatever they want to buttons without having to worry with Exceptions. Should I instead just make the set property do nothing? That could also lead to awkward results: myButton.Text = "abc"; MessageBox.Show(abc); //not "abc"! The general idea from the OO world is to in this kind of cases use Composition instead of inheritance. public class MySpecialButton : <Some class from System.Windows.Forms that already knows how to draw itself on forms> private Button button = new Button(); //I'd just draw this button on this class //and I'd then only show the fields I consider //relevant to the outside world. ... } But to make the Button "live" on a form it must inherit from some special class. I've looked on Control, but it seems to already have the Text property defined. I guess the ideal situation would be to inherit from some kind of class that wouldn't even have the Text property defined, but that'd have position, size, etc properties available. Upper in the hierarchy, after Control, we have Component, but that looks like a really raw class. Any clue about how to achieve this? I know this was a long post :( Thanks

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  • Communicating between classes

    - by zachary
    I have a form that is divided into two classes. Each class represents the widgets on part of the form. What is the best way to allow these classes to share data between each other and update each other. Example: Button in class A is clicked. Update text field in class C

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  • Determining where a function is defined in C#?

    - by templatetypedef
    Hey all - I am a complete novice at C# (I've never used it before) and recently needed to look over some code written in it. I spent the longest time trying to track down a nonexistent method in a class that didn't seem to be defined anywhere in the class that was using it. I later found out it was an "extension method," which I gather is a method grafted onto another class by some source. I completely understand the rationale behind this language feature and actually think it's quite nice. However, as someone without much experience in the language, it makes it harder to look up unfamiliar methods, since the method in question could be defined anywhere. My question is this: given an unfamiliar method call in C#, what's the best way for me to look up more info on it, given that it could be an extension method defined in an entirely separate class? Thanks!

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  • Can anybody explain the working of following code...?

    - by Siddhi
    Can anybody explain the working of following code...? interface myInterface{} public class Main { public static void main(String[] args) { System.out.println(new myInterface(){public String toString(){return "myInterfacetoString";}}); System.out.println(new myInterface(){public String myFunction(){return "myInterfacemyFunction";}}); } } Output is... myInterfacetoString primitivedemo.Main$2@9304b1 All answers saying that myInterface in println() statement is anonymous class. But as I already declared it as an interface, why does it allow me to create anonymous class of same name....? again...if these are anonymous classes then class main should allow me to give any name to these anonymous classes..But if try to do so..I'm getting compilation error

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  • Modifying an inherited Rails association

    - by Chris Kilmer
    I have a Team class that inherits from a Group class. Both Team and Groups have memberships through the same association. However, I need to run a method after a Team memberships is added but not a Group. I currently have something like this: class Group < ActiveRecord::Base has_many :memberships, :class_name => 'Connection', :foreign_key => 'connectable_id', :as => :connectable, :dependent => :destroy end class Team < Group has_many :memberships, :class_name => 'Connection', :foreign_key => 'connectable_id', :as => :connectable, :dependent => :destroy, :after_add => :add_company_membership private def membership_check(membership) end end Is there some way to modify the inherited association in Team so that I don't have to redefine the entire thing but rather just add the :after_add hook it? Any help would be appreciated.

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  • (Java) Get value of string loaded into dynamic-type object?

    - by Michael
    I'm very new to Java (~10 days), so my code is probably pretty bad, but here's what I've got: ArgsDataHolder argsData = new ArgsDataHolder(); // a class that holds two // ArrayList's where each element // representing key/value args Class thisArgClass; String thisArgString; Object thisArg; for(int i=2; i< argsString.length; i++) { thisToken = argsString[i]; thisArgClassString = getClassStringFromToken(thisToken).toLowerCase(); System.out.println("thisArgClassString: " + thisArgClassString); thisArgClass = getClassFromClassString(thisArgClassString); // find closing tag; concatenate middle Integer j = new Integer(i+1); thisArgString = getArgValue(argsString, j, "</" + thisArgClassString + ">"); thisArg = thisArgClass.newInstance(); thisArg = thisArgClass.valueOf(thisArgString); argsData.append(thisArg, thisArgClass); } The user basically has to input a set of key/value arguments into the command prompt in this format: <class>value</class>, e.g. <int>62</int>. Using this example, thisArgClass would be equal to Integer.class, thisArgString would be a string that read "62", and thisArg would be an instance of Integer that is equal to 62. I tried thisArg.valueOf(thisArgString), but I guess valueOf(<String>) is only a method of certain subclasses of Object. For whatever reason, I can't seem to be able to cast thisArg to thisArgClass (like so: thisArg = (thisArgClass)thisArgClass.newInstance();, at which point valueOf(<String>) should become accessible. There's got to be a nice, clean way of doing this, but it is beyond my abilities at this point. How can I get the value of the string loaded into a dynamically-typed object (Integer, Long, Float, Double, String, Character, Boolean, etc.)? Or am I just overthinking this, and Java will do the conversion for me? :confused:

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  • Dynamic class_name for has_many relations

    - by vooD
    I'm trying to make has_many relation with dynamic class_name attribute class Category < ActiveRecord::Base has_many :ads, :class_name => ( lambda { return self.item_type } ) end or class Category < ActiveRecord::Base has_many :ads, :class_name => self.item_type end But i got errors: can't convert Proc into String or undefined method `item_type' for #<Class:0xb62c6c88> Thank you for any help!

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  • Three customer addresses in one table or in separate tables?

    - by DR
    In my application I have a Customer class and an Address class. The Customer class has three instances of the Address class: customerAddress, deliveryAddress, invoiceAddress. Whats the best way to reflect this structure in a database? The straightforward way would be a customer table and a separate address table. A more denormalized way would be just a customer table with columns for every address (Example for "street": customer_street, delivery_street, invoice_street) What are your experiences with that? Are there any advantages and disadvantages of these approaches?

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  • A strange error in java generic.

    - by ???
    This is ok: Class<? extends String> stringClass = "a".getClass(); But this gets error: <T> void f(T obj) { Class<? extends T> objClass = obj.getClass(); } I know I can cast it like: <T> void f(T obj) { @SuppressWarnings("unchecked") Class<? extends T> objClass = (Class<? extends T>) obj.getClass(); } But why the previous error? Will the next release of Java 7 will support such usage?

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  • Django. Invalid keyword argument for this function. ManyToMany

    - by sagem_tetra
    I have this error: 'people' is an invalid keyword argument for this function class Passage(models.Model): name= models.CharField(max_length = 255) who = models.ForeignKey(UserProfil) class UserPassage(models.Model): passage = models.ForeignKey(Passage) people = models.ManyToManyField(UserProfil, null=True) class UserProfil(models.Model): user = models.OneToOneField(User) name = models.CharField(max_length=50) I try: def join(request): user = request.user user_profil = UserProfil.objects.get(user=user) passage = Passage.objects.get(id=2) #line with error up = UserPassage.objects.create(people= user_profil, passage=passage) return render_to_response('thanks.html') How to do correctly? Thanks!

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  • Make qwidget in new window in PyQt4

    - by matt
    I'm trying to make a class that extends qwidget, that pops up a new window, I must be missing something fundamental, class NewQuery(QtGui.QWidget): def __init__(self, parent): QtGui.QMainWindow.__init__(self,parent) self.setWindowTitle('Add New Query') grid = QtGui.QGridLayout() label = QtGui.QLabel('blah') grid.addWidget(label,0,0) self.setLayout(grid) self.resize(300,200) when a new instance of this is made in main window's class, and show() called, the content is overlaid on the main window, how can I make it display in a new window?

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  • PHP preg_match image between html tags

    - by Alvins
    I've got an html template like this: <div class="cont"> <div class="..."> <p>...<p> <img alt="" class="popup" src="DESIRED IMAGE LINK" style="..." /></p><p>...</p> .... And i want to extract "DESIRED IMAGE LINK" inside the "" tag, currently i'm using this: $pattern = '<div class="cont">.*?src=["\']?([^"\']?.*?(png|jpg|jpeg|gif))["\']?/i'; if (preg_match($pattern, $content, $image)) ..... But it doesn't work, the error is: warning: preg_match() [function.preg-match]: Unknown modifier '.' How can i fix it? Thanks

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  • pagination panel should remain static

    - by fusion
    i've a search form in which a user enters the keyword and the results are displayed with pagination. everything works fine except for the fact that when the user clicks on the 'Next' button, the pagination panel disappears as well when the page loads to retrieve the data through ajax. how do i make the pagination panel static, while the data is being retrieved? search.html: <form name="myform" class="wrapper"> <input type="text" name="q" id="q" onkeyup="showPage();" class="txt_search"/> <input type="button" name="button" onclick="showPage();" class="button"/> <p> </p> <div id="txtHint"></div> </form> ajax: var url="search.php"; url += "?q="+str+"&page="+page+"&list="; url += "&sid="+Math.random(); xmlHttp.onreadystatechange=stateChanged; xmlHttp.open("GET",url,true); xmlHttp.send(null); function stateChanged(){ if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete"){ document.getElementById("txtHint").innerHTML=xmlHttp.responseText; } //end if } //end function search.php: $self = $_SERVER['PHP_SELF']; $limit = 3; //Number of results per page $adjacents = 2; $numpages=ceil($totalrows/$limit); $query = $query." ORDER BY idQuotes LIMIT " . ($page-1)*$limit . ",$limit"; $result = mysql_query($query, $conn) or die('Error:' .mysql_error()); ?> <div class="search_caption">Search Results</div> <div class="search_div"> <table class="result"> <?php while ($row= mysql_fetch_array($result, MYSQL_ASSOC)) { $cQuote = highlightWords(htmlspecialchars($row['cQuotes']), $search_result); ?> <tr> . . .display results. . . </tr> <?php } ?> </table> </div> <hr> <div class="searchmain"> <?php //Create and print the Navigation bar $nav=""; $next = $page+1; $prev = $page-1; if($page > 1) { $nav .= "<a onclick=\"showPage('','$prev'); return false;\" href=\"$self?page=" . $prev . "&q=" .urlencode($search_result) . "\">< Prev</a>"; $first = "<a onclick=\"showPage('','1'); return false;\" href=\"$self?page=1&q=" .urlencode($search_result) . "\"> << </a>" ; } else { $nav .= "&nbsp;"; $first = "&nbsp;"; } for($i = 1 ; $i <= $numpages ; $i++) { if($i == $page) { $nav .= "<span class=\"no_link\">$i</span>"; }else{ $nav .= "<a onclick=\"showPage('',$i); return false;\" href=\"$self?page=" . $i . "&q=" .urlencode($search_result) . "\">$i</a>"; } } if($page < $numpages) { $nav .= "<a onclick=\"showPage('','$next'); return false;\" href=\"$self?page=" . $next . "&q=" .urlencode($search_result) . "\">Next ></a>"; $last = "<a onclick=\"showPage('','$numpages'); return false;\" href=\"$self?page=$numpages&q=" .urlencode($search_result) . "\"> >> </a>"; } else { $nav .= "&nbsp;"; $last = "&nbsp;"; } echo $first . $nav . $last; ?> </div>

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  • jquery XML, i need .html() not .text() but not working?

    - by Xtian
    I need var long to be exported as html and not text. I know I have .text() but when I use .html() it will not work. Also if I take the .text() out when declaring the variable and it will not work in IE? The reason for this is, in the XML certain words will have html tags like or and I need those to be recognized. I thought I solved it when I took out .text() but then i looked at IE and I got nothing. $(document).ready(function(){ $.ajax({ type: "GET", url: "xml/sites.xml", dataType: "xml", success: function(xml) { $(xml).find('site').each(function(){ var id = $(this).attr('id'); var title = $(this).find('title').text(); var class =$(this).find('class').text(); $('<div class="'+class+'" id="link_'+id+'"></div>').html('<h2>'+title+'</h2>').appendTo('#page-wrap'); $(this).find('desc').each(function(){ var long = $(this).find('long'); var url = $(this).find('url').text(); $('<div class="long"></div>').html(long).appendTo('#link_'+id); $('<a href="http://'+url+'"</a>').html(url).appendTo('#link_'+id); }); }); } }); });// JavaScript Document

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  • Extending abstract classes in c#

    - by ng
    I am a Java developer and I have noticed some differences in extending abstract classes in c# as opposed to Java. I was wondering how a c# developer would achived the following. 1) Covarience public abstract class A { public abstract List<B> List(); } public class BList : List<T> where T : B { } public abstract class C : A { public abstract BList List(); } So in the above hierarchy, there is covarience in C where it returns a type compatible with what A returns. However this gives me an error in Visual Studio. Is there a way to specify a covarient return type in c#? 2) Adding a setter to a property public abstract class A { public abstract String Name { get; } } public abstract class B : A { public abstract String Name { get; set } } Here the compiler complains of hiding. Any suggestions? Please do not suggest using interfaces unless that is the ONLY way to do this.

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  • How can I avoid huge communication classes in WCF?

    - by mafutrct
    My understanding is that all contract-implementing code has to be in a single class, that can become very large, obviously. How do I avoid this? I really prefer to have a few small classes doing one part of the communication with clients than a single behemoth class. The only idea I could think of is using multiple interfaces implemented by a single class split up by partial, but I don't this this is really solving the issue.

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  • Boost singleton trouble

    - by Ockonal
    Hi guys, I have some class which uses boost singleton. It calls some function from own c++ library. This library is written in make file as dependence. Now I have another singleton class and it should call first singleton class. After this code I got linkers error about undefined references for functions which are used in first singleton. When I remove calling first singleton class from second the errors remove. Maybe there is something wrong?

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  • Design classes/interface to support methods returning different types

    - by Nayn
    Hi, I have classes as below. public interface ITest <T> { public T MethodHere(); } public class test1 implements ITest<String> { String MethodHere(){ return "Bla"; } } public class test2 implements ITest<Integer> { Integer MethodHere(){ return Integer.valueOf(2); } } public class ITestFactory { public static ITest getInstance(int type) { if(type == 1) return new test1(); else if(type == 2) return new test2(); } } There is a warning in the factory class that ITest is used as raw type. What modification should I do to get rid of it? Thanks Nayn

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  • Misunderstanding function pointer - passing it as an argument

    - by Stef
    I want to pass a member function of class A to class B via a function pointer as argument. Please advise whether this road is leading somewhere and help me fill the pothole. #include <iostream> using namespace std; class A{ public: int dosomeA(int x){ cout<< "doing some A to "<<x <<endl; return(0); } }; class B{ public: B(int (*ptr)(int)){ptr(0);}; }; int main() { A a; int (*APtr)(int)=&A::dosomeA; B b(APtr); return 0; } This brilliant piece of code leaves me with the compiler error: cannot convert int (A::*)(int)' toint (*)(int)' in initialization Firstly I want it to compile. Secondly I don't want dosomeA to be STATIC.

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  • What to prefer in the following case?

    - by GK
    say suppose I have class as : public class Age { private int age; public int getAge() { return this.age; } } In my Main class I am calling the getAge() method many times. So I wanted to know is it advisable to call so many times or call once and assign it to some variable and use that variable. Which is best and why?

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  • jQueryUI widget text plus icon

    - by cf_PhillipSenn
    I have: <div class="ui-widget"> <div class="ui-widget-header"> My Menu<span class="ui-icon ui-icon-circle-triangle-n"></span> </div> <ul class="ui-widget-content"> <li>Menu Item 1</li> <li>Menu Item 2</li> <li>Menu Item 3</li> </ul> </div> Right now, the ui-icon is appearing below "My Menu" Q: How can I get "My Menu" to appear on the same line as the UI widget?

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  • Mock implementations in C++

    - by forneo
    Hi guys, I need a mock implementation of a class - for testing purposes - and I'm wondering how I should best go about doing that. I can think of two general ways: Create an interface that contains all public functions of the class as pure virtual functions, then create a mock class by deriving from it. Mark all functions (well, at least all that are to be mocked) as virtual. I'm used to doing it the first way in Java, and it's quite common too (probably since they have a dedicated interface type). But I've hardly ever seen such interface-heavy designs in C++, thus I'm wondering. The second way will probably work, but I can't help but think of it as kind of ugly. Is anybody doing that? If I follow the first way, I need some naming assistance. I have an audio system that is responsible for loading sound files and playing the loaded tracks. I'm using OpenAL for that, thus I've called the interface "Audio" and the implementation "OpenALAudio". However, this implies that all OpenAL-specific code has to go into that class, which feels kind of limiting. An alternative would be to leave the class' name "Audio" and find a different one for the interface, e.g. "AudioInterface" or "IAudio". Which would you suggest, and why?

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  • Unable to run JAR file (created in Eclipse)

    - by Trist
    I hate starting a post with this but I'm new to Java... I've followed this tutorial to create a socket server (mines in Eclipse). I can run the server within Eclipse, all is well. But when I try to export the project I can't figure out how to run it. I keep getting this error (it varies depending on how I run it) Exception in thread "main" java.lang.NoClassDefFoundError: xsocketserver/Main Caused by: java.lang.ClassNotFoundException: xsocketserver.Main at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:188) at java.lang.ClassLoader.loadClass(ClassLoader.java:315) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:330) at java.lang.ClassLoader.loadClass(ClassLoader.java:250) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:398) I've read this problem relates to class paths being set. I've tried the following: java -cp libs/xSocket-2.8.12.jar xsocketserver.Main java -jar xSocketServer.jar java -classpath xSocketServer:xSocketServer/libs/xSocket-2.8.12.jar xsocketserver.Main plus many others. The file structure within the JAR is as follows: xSocketServer.jar -> xsocketserver -> Main.class -> xSocketDataHandler.class -> META-INF -> MANIFEST.MF -> libs -> xSocket-2.8.12.jar Incidentally I've tried adding my own manifest file which contains the Class-Path but when I check it it always reads: Manifest-Version: 1.0 Main-Class: xsocketserver.Main I'm guessing this is a common problem based on the number of hits I've seen in Google but I can't fathom what I'm doing wrong. Wrong Export settings maybe??

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  • java.util.Observable, will clients complete executing their update() before continuing

    - by jax
    When I call: setChanged(); notifyObservers() on a java.until.Observable class, will all the listening Observer objects complete execution of their udpate() methods - assuming we are running in the same Thread - before the java.until.Observable class continues running? This is important because I will be sending a few messages through the notifyObservers(Object o) method in quick concession, it is important that each Observer class has finished its method before the new one though. I understand that the order of execution for each Observer class may vary when we call notifyObservers() - it is just important that the order of method execution for each individual instance is in order.

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