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• Significant amount of the time, I can't think of a reason to have an object instead of a static class. Do objects have more benefits than I think?

  - by Prog

  I understand the concept of an object, and as a Java programmer I feel the OO paradigm comes rather naturally to me in practice. However recently I found myself thinking: Wait a second, what are actually the practical benefits of using an object over using a static class (with proper encapsulation and OO practices)? I could think of two benefits of using an object (both significant and powerful): Polymorphism: allows you to swap functionality dynamically and flexibly during runtime. Also allows to add new functionality 'parts' and alternatives to the system easily. For example if there's a Car class designed to work with Engine objects, and you want to add a new Engine to the system that the Car can use, you can create a new Engine subclass and simply pass an object of this class into the Car object, without having to change anything about Car. And you can decide to do so during runtime. Being able to 'pass functionality around': you can pass an object around the system dynamically. But are there any more advantages to objects over static classes? Often when I add new 'parts' to a system, I do so by creating a new class and instantiating objects from it. But recently when I stopped and thought about it, I realized that a static class would do just the same as an object, in a lot of the places where I normally use an object. For example, I'm working on adding a save/load-file mechanism to my app. With an object, the calling line of code will look like this: Thing thing = fileLoader.load(file); With a static class, it would look like this: Thing thing = FileLoader.load(file); What's the difference? Fairly often I just can't think of a reason to instantiate an object when a plain-old static-class would act just the same. But in OO systems, static classes are fairly rare. So I must be missing something. Are there any more advantages to objects other from the two that I listed? Please explain.

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• What am I not getting about this abstract class implementation?

  - by Schnapple

  PREFACE: I'm relatively inexperienced in C++ so this very well could be a Day 1 n00b question. I'm working on something whose long term goal is to be portable across multiple operating systems. I have the following files: Utilities.h #include <string> class Utilities { public: Utilities() { }; virtual ~Utilities() { }; virtual std::string ParseString(std::string const& RawString) = 0; }; UtilitiesWin.h (for the Windows class/implementation) #include <string> #include "Utilities.h" class UtilitiesWin : public Utilities { public: UtilitiesWin() { }; virtual ~UtilitiesWin() { }; virtual std::string ParseString(std::string const& RawString); }; UtilitiesWin.cpp #include <string> #include "UtilitiesWin.h" std::string UtilitiesWin::ParseString(std::string const& RawString) { // Magic happens here! // I'll put in a line of code to make it seem valid return ""; } So then elsewhere in my code I have this #include <string> #include "Utilities.h" void SomeProgram::SomeMethod() { Utilities *u = new Utilities(); StringData = u->ParseString(StringData); // StringData defined elsewhere } The compiler (Visual Studio 2008) is dying on the instance declaration c:\somepath\somecode.cpp(3) : error C2259: 'Utilities' : cannot instantiate abstract class due to following members: 'std::string Utilities::ParseString(const std::string &)' : is abstract c:\somepath\utilities.h(9) : see declaration of 'Utilities::ParseString' So in this case what I'm wanting to do is use the abstract class (Utilities) like an interface and have it know to go to the implemented version (UtilitiesWin). Obviously I'm doing something wrong but I'm not sure what. It occurs to me as I'm writing this that there's probably a crucial connection between the UtilitiesWin implementation of the Utilities abstract class that I've missed, but I'm not sure where. I mean, the following works #include <string> #include "UtilitiesWin.h" void SomeProgram::SomeMethod() { Utilities *u = new UtilitiesWin(); StringData = u->ParseString(StringData); // StringData defined elsewhere } but it means I'd have to conditionally go through the different versions later (i.e., UtilitiesMac(), UtilitiesLinux(), etc.) What have I missed here?

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• Can I use an abstract class instead of a private __construct() when creating a singleton in PHP?

  - by Pheter

  When creating a Singleton in PHP, I ensure that it cannot be instantiated by doing the following: class Singleton { private function __construct() {} private function __clone() {} public static function getInstance() {} } However, I realised that defining a class as 'abstract' means that it cannot be instantiated. So is there anything wrong with doing the following instead: abstract class Singleton { public static function getInstance() {} } The second scenario allows me to write fewer lines of code which would be nice. (Not that it actually makes much of a difference.)

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• Is it possible for an abstract class to force it's children to have a constructor in PHP?

  - by Logan Serman

  I would like to do something like this: abstract class Foo { public function __construct() { echo 'This is the parent constructor'; } abstract function __construct(); } class Bar extends Foo { // constructor is required as this class extends Foo public function __construct() { //call parent::__construct() if necessary echo 'This is the child constructor'; } } But I get a fatal error when doing this: Fatal error: Cannot redeclare Foo::__construct() in Foo.php on line 8 Is there another way to ensure child classes have a constructor?

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• Liskov substitution and abstract classes / strategy pattern

  - by Kolyunya

  I'm trying to follow LSP in practical programming. And I wonder if different constructors of subclasses violate it. It would be great to hear an explanation instead of just yes/no. Thanks much! P.S. If the answer is no, how do I make different strategies with different input without violating LSP? class IStrategy { public: virtual void use() = 0; }; class FooStrategy : public IStrategy { public: FooStrategy(A a, B b) { c = /* some operations with a, b */ } virtual void use() { std::cout << c; } private: C c; }; class BarStrategy : public IStrategy { public: BarStrategy(D d, E e) { f = /* some operations with d, e */ } virtual void use() { std::cout << f; } private: F f; };

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• Is there a good design pattern for this messaging class?

  - by salonMonsters

  Is there a good design pattern for this? I want to create a messaging class. The class will be passed: the type of message (eg. signup, signup confirmation, password reminder etc) the client's id The class needs to then look up the client's messaging preferences in the db (whether they want communication by email, sms or both) Then depending on the client's preference it will format the message for the medium (short version for sms, long form for email) and send it through our mail or sms provider's API. Because the fact that we want to be able to change out email and sms providers if need be I wondered if the Command Pattern would be a good choice.

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• Visibility of nester class constructor

  - by user295502

  Is there a way to limit the instantiation of the nested class in C#? I want to prevent nested class being instantiated from any other class except the nesting class, but to allow full access to the nested class from other code.

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• access exception when invoking method of an anonymous class using java reflection

  - by Asaf David

  Hello I'm trying to use an event dispatcher to allow a model to notify subscribed listeners when it changes. the event dispatcher receives a handler class and a method name to call during dispatch. the presenter subscribes to the model changes and provide a Handler implementation to be called on changes. Here's the code (I'm sorry it's a bit long). EventDispacther: package utils; public class EventDispatcher<T> { List<T> listeners; private String methodName; public EventDispatcher(String methodName) { listeners = new ArrayList<T>(); this.methodName = methodName; } public void add(T listener) { listeners.add(listener); } public void dispatch() { for (T listener : listeners) { try { Method method = listener.getClass().getMethod(methodName); method.invoke(listener); } catch (Exception e) { System.out.println(e.getMessage()); } } } } Model: package model; public class Model { private EventDispatcher<ModelChangedHandler> dispatcher; public Model() { dispatcher = new EventDispatcher<ModelChangedHandler>("modelChanged"); } public void whenModelChange(ModelChangedHandler handler) { dispatcher.add(handler); } public void change() { dispatcher.dispatch(); } } ModelChangedHandler: package model; public interface ModelChangedHandler { void modelChanged(); } Presenter: package presenter; public class Presenter { private final Model model; public Presenter(Model model) { this.model = model; this.model.whenModelChange(new ModelChangedHandler() { @Override public void modelChanged() { System.out.println("model changed"); } }); } } Main: package main; public class Main { public static void main(String[] args) { Model model = new Model(); Presenter presenter = new Presenter(model); model.change(); } } Now, I except to get the "model changed" message. However, I'm getting an java.lang.IllegalAccessException: Class utils.EventDispatcher can not access a member of class presenter.Presenter$1 with modifiers "public". I understand that the class to blame is the anonymous class i created inside the presenter, however I don't know how to make it any more 'public' than it currently is. If i replace it with a named nested class it seem to work. It also works if the Presenter and the EventDispatcher are in the same package, but I can't allow that (several presenters in different packages should use the EventDispatcher) any ideas?

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• Cocoa class not displaying data in NSWindow

  - by Matt S.

  I have one class that controls one window, and another class that controls a different window in the same xib, however, the second window never displays what it should. In the first class I alloc and init the second class, then pass some information to it. In the second class it displays that data in the table view. Yes, in the .xib I have all the connections set up correctly, I've quadruple checked. Also the code is correct, same with the connections, I've quadruple checked.

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• PHP object class variable

  - by mck89

  I have built a class in PHP and I must declare a class variable as an object. Everytime I want to declare an empty object I use: $var=new stdClass; But if I use it to declare a class variable as class foo { var $bar=new stdClass; } a parse error occurs. Is there a way to do this or must I declare the class variable as an object in the constructor function? PS: I'm using PHP 4.

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• Problem with OOP Class Definitions

  - by oben

  Hi, this is Oben from Turkey. I work for my homework in C++ and i have some problems with multiply definitions. My graph class ; class Graph{ private: string name; //Graph name fstream* graphFile; //Graph's file protected: string opBuf; //Operations buffer int containsNode(string); //Query if a node is present Node* nodes; //Nodes in the graph int nofNodes; //Number of nodes in the graph public: static int nOfGraphs; //Number of graphs produced Graph(); //Constructors and destructor Graph(int); Graph(string); Graph(const Graph &); ~Graph(); string getGraphName(); //Get graph name bool addNode(string); //add a node to the graph bool deleteNode(string); //delete a node from the graph bool addEdge(string,string); //add an edge to the graph bool deleteEdge(string,string); //delete an edge from the graph void intersect(const Graph&); //intersect the graph with the <par> void unite(const Graph&); //intersect the graph with the <par> string toString(); //get string representation of the graph void acceptTraverse(BreadthFirst*); void acceptTraverse(DepthFirst *); }; and my traversal class; class Traversal { public: string *visitedNodes; virtual string traverse (const Graph & ); }; class BreadthFirst : public Traversal { public : BreadthFirst(); string traverse(); }; class DepthFirst : public Traversal { public : DepthFirst(); string traverse(); }; My problem is in traversal class , i need to declare Graph class at the same time , in graph class i need traversal class to declare. I have big problems with declerations :) Could you please help me ?

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• Cannot access Class methods from previous windows form - C#

  - by George

  I am writing an app, still, where I need to test some devices every minute for 30 minutes. It made sense to use a timer set to kick off every 60 secs and do whats required in the event handler. However, I need the app to wait for the 30 mins until I have finished with the timer since the following code alters the state of the devices I am trying to monitor. I obviously don't want to use any form of loop to do this. I thought of using another windows form, since I also display the progress, which will simply kick off the timer and wait until its complete. The problem I am having with this is that I use a device Class and cant seem to get access to the methods in the device class from the 2nd (3rd actually - see below) windows form. I have an initial windows form where I get input from the user, then call the 2nd windows form where it work out which tests need to be done and which device classes need to be used, and then I want to call the 3rd windows form to handle the timer. I will have up to 6-7 device classes and so wanted to only instantiate them when actually requiring them, from the 2nd form. Should I have put this logic into the 1st windows form (program class ??) ? Would I not still have the problem of not being able to access device class methods from there too ? Anyway, perhaps someone knows of a better way to do the checks every minute without the rest of the code executing (and changing the status of the devices) or how I should be accessing the methods in the app ?? Well that's the problem, I cant get that part of it to work correctly. Here is the definition for the calling form including the device class - namespace NdtStart { public partial class fclsNDTCalib : Form { NDTClass NDT = new NDTClass(); public fclsNDTCalib() (new fclsNDTTicker(NDT)).ShowDialog(); Here is the class def for the called form - namespace NdtStart { public partial class fclsNDTTicker : Form { public fclsNDTTicker() I tried lots but couldn't get the arguments to work.

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• Jquery adding and removing class dynamically

  - by user244394

  I am trying to add the class"selected" when a link is clicked and when the user click on the next link , I want to remove the previously "selected" class and add "selected" to the link clicked.. -Thanks in advance $(document).ready(function() { $('.news a').click(function(){ $(this).addClass("selected"); }); }); <div class="news-w"> <div class="news" id="getnews-1"> <a href="#" >topic</a> </div> <div class="news" id="getnews-2"> <a href="#">topic</a> </div> <div class="news" id="getnews-3"> <a href="#" >topic</a> </div> <div class="news" id="getnews-4"> <a href="#">topic</a> </div> <div class="news" id="getnews-5"> <a href="#">topic</a> </div> </div>

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• Is there a case for parameterising using Abstract classes rather than Interfaces?

  - by Chris

  I'm currently developing a component based API that is heavily stateful. The top level components implement around a dozen interfaces each. The stock top-level components therefore sit ontop of a stack of Abstract implementations which in turn contain multiple mixin implementations and implement multiple mixin interfaces. So far, so good (I hope). The problem is that the base functionality is extremely complex to implement (1,000s of lines in 5 layers of base classes) and therefore I do not wish for component writers to implement the interfaces themselves but rather to extend my base classes (where all the boiler plate code is already written). If the API therefore accepts interfaces rather than references to the Abstract implementation that I wish for component writers to extends, then I have a risk that the implementer will not perform the validation that is both required and assumed by other areas of code. Therefore, my question is, is it sometimes valid to paramerise API methods using an abstract implementation reference rather than a reference to the interface(s) that it implements? Do you have an example of a well-designed API that uses this technique or am I trying to talk myself into bad-practice?

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• Remove second class from an element and add another class

  - by rahul

  Hi, $(document).ready ( function () { $(".MenuItem").mouseover ( function () { // Remove second class and add another class [ Maintain MenuItem class ] // Eg: For div1 remove Sprite1 and then add Sprite1Dis and for div2 // remove Sprite2 and add Spprite2Dis }); $(".MenuItem").mouseout ( function () { // Reverse of mouseover. ie Remove Sprite1Dis and add Sprite1 }); }); <div id="div1" class="MenuItem Sprite1"> &nbsp; </div> <div id="div2" class="MenuItem Sprite2"> &nbsp; </div> <div id="div3" class="MenuItem Sprite3"> &nbsp; </div> <div id="div4" class="MenuItem Sprite4"> &nbsp; </div> <div id="div5" class="MenuItem Sprite5"> &nbsp; </div> <div id="div6" class="MenuItem Sprite6"> &nbsp; </div> My problem is listed as comment inside the code section. What will be the easiest way to achieve this? Thanks in advance

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• Which is better: many class definitions in the same file or every class definition in a separate file?

  - by Javed Akram

  Which is better: many class definitions in same file or every class definition in separate file? Examples: 1) Many classes in same file. Say, myManyClasses.cs: namespace myPack { class myClass1() { } class myClass2() { } class myClass3() { } . . . } 2) Every class in separate file: myClass1.cs namespace myPack { class myClass1() { } } myClass2.cs namespace myPack { class myClass2() { } } . . .

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• NetBeans 6.8/6.7 UML Class Diagrams

  - by ikurtz

  i have tried to generate Class Diagrams in NetBeans 6.7 and 6.8 but all i get is: i figured out installing UML for 6.8 here: NetBeans 6.8 UML i have followed the instructions here: UML Class diagrams i so far i failed to generate anything meaningful. i have followed the tips: Open your project, then create a new UML project (choose "Reverse Engineered Java-Platform model"). After that all your classes will be available in the UML project under "Model". You can now create a new class diagram and drag your classes from "Model" onto the diagram. but nothing meaningful happens when i drag my classes to the Class Diagrams. it always represents the classes as "datatype" on the diagram and class info is not displayed. any helpful tips regarding how can i fix this? or another way of generating Java class diagrams? thank you for your time.

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• change the class loading order google app engine java

  - by Shekhar

  I am trying to create an application on google app engine using struts2. Struts2 internally uses freemarker .One of the Freemarker framework classes suppose X internally uses a class javax.swing.Treenode which is not in google app engine jre white list. Now in order to run my application i created a new class X in the same package structure as it was in freemarker framework and copied the class to WEB-INF classes.Then When i run my application it run fine. The problem is that i want to take out the class X from my application sourcecode and move it to newly created jar and place it in WEB-INF/lib folder. So that i can reuse the code in multiple project and my code remains clean of the freemarker code. But when i run the application it picks the old class X from the original freemarker framework.As a result i get ClassNotFoundException. Can anyone provide any help such that i can change the ClassLoading order such that my jar containing X class loads first.

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• ZipArchive php Class - Does it support all servers?

  - by SoLoGHoST

  Ok, just wondering on the versions of PHP that this class is built into. And if they are built into all platforms (OS's). I'm wanting an approach to search through a zip file and place files using file_put_contents in different filepaths within the webroot. In any case, I'm familiar with how to do this with the ZipArchive class, but I'm wondering if using this class would be a good solution and support MOST, if not ALL servers?? I mean, I'd rather not use a method that requires the Server to have it installed. I'm looking for a solution to this that will support at least MOST servers without having to install the class... Thanks :) Also, I'd like to support opening tar.gz and/or .tgz files if possible, but I don't think the ZipArchive class supports this, but perhaps a different built-in php class does??

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• Class Methods Inheritence

  - by Roman A. Taycher

  I was told that static methods in java didn't have Inheritance but when I try the following test package test1; public class Main { /** * @param args the command line arguments */ public static void main(String[] args) { TB.ttt(); TB.ttt2(); } } package test1; public class TA { static public Boolean ttt() { System.out.println("TestInheritenceA"); return true; } static public String test ="ClassA"; } package test1; public class TB extends TA{ static public void ttt2(){ System.out.println(test); } } it printed : TestInheritenceA ClassA so do java static methods (and fields have) inheritance (if you try to call a class method does it go down the inheritance chai looking for class methods). Was this ever not the case,are there any inheritance OO languages that are messed up like that for class methods?

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• C++ Class Inheritance architecture - preventing casting

  - by Some One

  I have a structure of base class and a couple of inherited classed. Base class should be pure virtual class, it should prevent instantiation. Inherited classes can be instantiated. Code example below: class BaseClass { public: BaseClass(void); virtual ~BaseClass(void) = 0; }; class InheritedClass : public BaseClass { public: InheritedClass1(void); ~InheritedClass1(void); }; class DifferentInheritedClass : public BaseClass { public: DifferentInheritedClass(void); ~DifferentInheritedClass(void); }; I want to prevent the following operations to happen: InheritedClass *inherited1 = new InheritedClass(); DifferentInheritedClass *inherited2 = new DifferentInheritedClass (); BaseClass *base_1 = inherited1; BaseClass *base_2 = inherited2; *base_1 = *base_2;

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• method __getattr__ is not inherited from parent class

  - by ??????

  Trying to subclass mechanize.Browser class: from mechanize import Browser class LLManager(Browser, object): IS_AUTHORIZED = False def __init__(self, login = "", passw = "", *args, **kwargs): super(LLManager, self).__init__(*args, **kwargs) self.set_handle_robots(False) But when I make something like this: lm["Widget[LinksList]_link_1_title"] = anc then I get an error: Traceback (most recent call last): File "<pyshell#8>", line 1, in <module> lm["Widget[LinksList]_link_1_title"] = anc TypeError: 'LLManager' object does not support item assignment Browser class have overridden method __getattr__ as shown: def __getattr__(self, name): # pass through _form.HTMLForm methods and attributes form = self.__dict__.get("form") if form is None: raise AttributeError( "%s instance has no attribute %s (perhaps you forgot to " ".select_form()?)" % (self.__class__, name)) return getattr(form, name) Why my class or instance don't get this method as in parent class?

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• jQuery to target CSS a:hover class

  - by songdogtech

  Confused here. What's the best way to change the hover CSS of the link below, and how? toggle.Class? add.Class? I want to show an image on hover. I have been able to change the color of the text with $("#menu-item-1099 a:contains('rss')").css("color", "#5d5d5d"); but can't seem to target the hover class. <div id="access"> <div class="menu-header"> <ul id="menu-main-menu" class="menu"> <li id="menu-item-1099" class="menu-item menu-item-type-custom menu-item-1099"> <a href="http://mydomain.com/feed/">rss</a></li>

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• Testing for the existence of a field in a class

  - by Brett

  Hi, i have a quick question. I have a 2D array that stores an instance of a class. The elements of the array are assigned a particular class based on a text file that is read earlier in the program. Since i do not know without looking in the file what class is stored at a particular element i could refer to a field that doesn't exist at that index (referring to appearance when an instance of temp is stored in that index). i have come up with a method of testing this, but it is long winded and requires a second matrix. Is there a function to test for the existence of a field in a class? class temp(): name = "default" class temp1(): appearance = "@"

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• Create Generic Class Instance from Static Method in a Derived Class

  - by user343547

  I have a class in C# with a template and static method similar to class BClass<T> { public static BClass<T> Create() { return new BClass<T>(); } } From this I derive a class and specify a template parameter to the base class class DClass : BClass<int> { } A problem occurs when I try to use the static method to create an instance of D class Program { static void Main(string[] args) { DClass d = DClass.Create(); } } Gives a compiler error "Cannot implicitly convert type 'Test.BClass<int ' to 'Test.DClass'." Adding the below cast leads to a runtime casting exception. DClass d = (DClass)DClass.Create(); Is there any succint way to allow the static method to create instances of the derived class? Ideally I would like the equivalent of a c++ typedef and I don't want the below syntax (which does work). BClass<int> d = DClass.Create();

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