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• Using enums or a set of classes when I know I have a finite set of different options?

  - by devoured elysium

  Let's say I have defined the following class: public abstract class Event { public DateTime Time { get; protected set; } protected Event(DateTime time) { Time = time; } } What would you prefer between this: public class AsleepEvent : Event { public AsleepEvent(DateTime time) : base(time) { } } public class AwakeEvent : Event { public AwakeEvent(DateTime time) : base(time) { } } and this: public enum StateEventType { NowAwake, NowAsleep } public class StateEvent : Event { protected StateEventType stateType; public MealEvent(DateTime time, StateEventType stateType) : base(time) { stateType = stateType; } } and why? I am generally more inclined to the first option, but I can't explain why. Is it totally the same or are any advantages in using one instead of the other? Maybe with the first method its easier to add more "states", altough in this case I am 100% sure I will only want two states: now awake, and now asleep (they signal the moments when one awakes and one falls asleep).

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• Should I create protected constructor for my singleton classes?

  - by Vijay Shanker

  By design, in Singleton pattern the constructor should be marked private and provide a creational method retuning the private static member of the same type instance. I have created my singleton classes like this only. public class SingletonPattern {// singleton class private static SingletonPattern pattern = new SingletonPattern(); private SingletonPattern() { } public static SingletonPattern getInstance() { return pattern; } } Now, I have got to extend a singleton class to add new behaviors. But the private constructor is not letting be define the child class. I was thinking to change the default constructor to protected constructor for the singleton base class. What can be problems, if I define my constructors to be protected? Looking for expert views....

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• How to implement Voting for Grails Domain Classes?

  - by userWebMobile

  I have a Book class and need to implement a yes/no voting functionality. My domain classes look like this: class Book { String title static hasMany = [votes: Vote] } class User { String name static hasMany = [votes: Vote] } class Vote { boolean yesVote static belongsTo = [user: User, book: Book] } What is the best way to implement a voting for the book class. I need the following informations: What is the average yesVote for a book over all votes (either yes or no)? How to check if a specific user has done a vote? What is the best way to implement the computation of the average yesVote such that the performance does not drop?

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• Removing items from lists and all references to them.

  - by LiamV

  I'm facing a situation where I have dependent objects and I would like to be able to remove an object and all references to it. Say I have an object structure like the code below, with a Branch type which references two Nodes. public class Node { // Has Some Data! } public class Branch { // Contains references to Nodes public Node NodeA public Node NodeB } public class Graph { public List<Node> Nodes; public List<Branch> Branches; } If I remove a Node from the Nodes list in the Graph class, it is still possible that one or more Branch objects still contains a reference to the removed Node, thus retaining it in memory, whereas really what I would quite like would be to set any references to the removed Node to null and let the garbage collection kick in. Other than enumerating through each Branch and checking each Node reference sequentially, are there any smart ideas on how I remove references to the Node in each Branch instance AND indeed any other class which reference the removed Node?

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• WithEvents LinkedList is it Impossible?

  - by serhio

  What is the optimal approach to a WithEvents Collection - VB.NET? Have you any remarks on the code bellow (skipping the Nothing verifications)? The problem is when I obtain the LinkedListNode(Of Foo) in a For Each block I can set myNode.Value = something, and here is a handlers leak... -Could I override the FooCollection's GetEnumerator in this case? -No. :( cause NotInheritable Class LinkedListNode(Of T) Class Foo Public Event SelectedChanged As EventHandler End Class Class FooCollection Inherits LinkedList(Of Foo) Public Event SelectedChanged As EventHandler Protected Overloads Sub AddFirst(ByVal item As Foo) AddHandler item.SelectedChanged, AddressOf OnSelectedChanged MyBase.AddFirst(item) End Sub Protected Overloads Sub AddLast(ByVal item As Foo) AddHandler item.SelectedChanged, AddressOf OnSelectedChanged MyBase.AddLast(item) End Sub ' ------------------- ' Protected Overloads Sub RemoveFirst() RemoveHandler MyBase.First.Value.SelectedChanged, _ AddressOf OnSelectedChanged MyBase.RemoveFirst() End Sub Protected Overloads Sub RemoveLast(ByVal item As Foo) RemoveHandler MyBase.Last.Value.SelectedChanged, _ AddressOf OnSelectedChanged MyBase.RemoveLast() End Sub ' ------------------- ' Protected Sub OnSelectedChanged(ByVal sender As Object, ByVal e As EventArgs) RaiseEvent SelectedChanged(sender, e) End Sub End Class

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• creating BeanInfo objects in NetBeans 6.1 does not work for some objects

  - by Coder

  I have recently learned about BeanInfo classes in Java, and have successfully used them to add icons to my custom GUI components which extend swing components such as JTextField, however i have a more specialized GUI component which extends from another one of my GUI components, which then extends from JTextField. Ie. the class hierarchy is of the form "A - B - JTextField". I can create a bean info object that works for class B, but when i click on the bean info editor option in netbeans to create a bean info object for class A, nothing happens. Ie. there is no error pop-up and a bean info object is not created. There isn't much difference between class A and B. Both A and B have default no argument constructors and they are very similar to each other. The only thing i can really think of is that A uses generics and B does not. I would like to create a beaninfo object for class A so that i can add custom icons for that component. Any help would be appreciated. Thanks.

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• django forms from two tables referencial integrity

  - by dana

  i have a class named cv,and a class named university, and each user that completes his cv, should choose a University he studyes at. My problem is: one student can study at one or 2 or three universities, or may be a user that is not student. I need to take this data into a form, and i use ModelForm. The data from the Cv class, and from the University class in the same form, and the user can add one or more universities, or no university. (in the same form) How should i do it? Should i use ModelForm? if i have a foreign key in the CV class, and the user is not a student (so he is at zero universities), i may get an referencial integrity error. thanks a lot

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• Rails Model for Playlist that can contain tracks and albums using polymorphism

  - by philk

  I struggle to find a model how to store a playlist with different type of items on it in Rails. Consider I have class Track end class Album has_many :tracks end class PlaylistItem belongs_to :playable belongs_to :playlist end class Playable belongs_to :playable, :polymorph => true end class Playlist has_many :playlist_items end I think I can use a polymorphic model "Playable" here since the Playlist can contain Tracks, Albums and maybe in the future also Movies. Also I would like to use STI for Track and Albums since they share some common attributes like title and length but also have totally different attributes. I modeled it like described here but it does not work. Anybody any idea how to model a Playlist that can contain many items of different kind?

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• jquery: addClass 1,2,3 etc. auto to a list

  - by Svensson

  Hello, is it possible, to add auto numeric classes to a list by using jquery? html: <ul id="list"> <li>Element 1</li> <li>Element 2</li> <li>Element 3</li> <li>Element 4</li> <li>Element 5</li> </ul> i want to get something like this: <ul id="list"> <li class="1">Element 1</li> <li class="2">Element 2</li> <li class="3">Element 3</li> <li class="4">Element 4</li> <li class="5">Element 5</li> </ul> hope there is a solution available :-)

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• Is it possible to create nested classes in PHP as it is in C#?

  - by Edward Tanguay

  In C# you can have nested classes like this, which are useful if you have classes which do not have meaning outside the scope of one particular class, e.g. in a factory pattern: public abstract class BankAccount { private BankAccount() {} private sealed class SavingsAccount : BankAccount { ... } private sealed class CheckingAccount : BankAccount { ... } public BankAccount MakeSavingAccount() { ... } public BankAccount MakeCheckingAccount() { ... } } Is this possible in PHP? I've read that it was planned for PHP 5, then cancelled, then planned again, but can't find definitive info. Does anyone know how to create nested classes (classes within the scope of another class) as in the above C# example using PHP 5.3?

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• Guice ThrowingProvider problem

  - by KARASZI István

  According to the ThrowingProvider documentation of Guice I have the following interface: public interface IConfigurableProvider<T> extends ThrowingProvider<T, ConfigException> {} I have multiple classes that implements this interface, let assume I have the following: public class SomethingProvider extends ConfiguredProvider implements IConfigurableProvider<Something> {} Of course this class implements the necessary method: public Something get() throws ConfigException { /* ... */ } In my module, I have the following code in MyModule.java ThrowingProviderBinder.create(binder()) .bind(IConfigurableProvider.class, Something.class) .to(SomethingProvider.class); But when I start my application the following error produced: 6) No implementation for com.package.Something was bound. while locating com.package.Something for parameter 5 at com.package.OtherClass.<init>(OtherClass.java:78) at com.package.MyModule.configure(MyModule.java:106) I don't really know where should I start looking for the bug.

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• app_label in an abstract Django model

  - by rayan

  Hi all, I'm trying to get an abstract model working in Django and I hit a brick wall trying to set the related_name per the recommendation here: http://docs.djangoproject.com/en/dev/topics/db/models/#be-careful-with-related-name This is what my abstract model looks like: class CommonModel(models.Model): created_on = models.DateTimeField(editable=False) creared_by = models.ForeignKey(User, related_name="%(app_label)s_%(class)s_created", editable=False) updated_on = models.DateTimeField(editable=False) updated_by = models.ForeignKey(User, related_name="%(app_label)s_%(class)s_updated", editable=False) def save(self): if not self.id: self.created_on = datetime.now() self.created_by = user.id self.updated_on = datetime.now() self.updated_by = user.id super(CommonModel, self).save() class Meta: abstract = True My common model is in [project_root]/models.py. It is the parent object of this model, which is located in an app called Feedback [project_root]/feedback/models.py: from django.db import models from mediasharks.models import CommonModel class Feedback(CommonModel): message = models.CharField(max_length=255) request_uri = models.CharField(max_length=255) domain = models.CharField(max_length=255) feedback_type = models.IntegerField() Basically I'm trying to set up a common model so that I'll always be able to tell when and by whom database entries were created. When I run "python manage.py validate" I get this error message: KeyError: 'app_label' Am I missing something here?

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• TypeError: Error #1009 Actionscript 3 help.

  - by matt_t

  I am extremely frustrated. I'm following a tutorial and mimicing it on my own. I've been able to sort out most of the errors so far but this one has me stumped. I have tried replacing all of the class files with the tutorial specimen ones but i still get the error. TypeError: Error #1009: Cannot access a property or method of a null object reference. at com.senocular.utils::KeyObject/construct() at com.senocular.utils::KeyObject() at com.asgamer.basics1::Ship() at com.asgamer.basics1::Engine() Now, not really understanding the error properly I paste dumped the files online for you to look at. Ship class: textbin.com/78z35 Engine class: textbin.com/32b24 KeyObject class: textbin.com/p2725 As the error still occured when using the specimen class files I really have no idea where to begin. I will gladly try out any suggestions (although later on, i'm tired now ;). Thanks very much.

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• Tab on hover mode while mouse over drop down menu

  - by Hwang

  How could I have the tab to be on hover mode while I rollover the drop down sub-menu. Does it require javascript or it could be done solely on CSS? <li id="anchor" class="title dropdown"><a href="#">Main Tab</a> <div class="column"> <ul> <li class="subtitle">Button 1</li> <li class="subtitle">Button 2</li> <li class="subtitle">Button 3</li> </div> </li>

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• Question on a tutorial

  - by hansa

  Hello, i´m trying to get following tutorial to run and understand: http://www.ibm.com/developerworks/web/library/wa-cometjava/index.html In the example code which can be downloaded at the bottom of the page is everything in one class with two inner classes. How can i make the the thread of "MessageSender" (Listing 3) visible to "The Weatherman" (Listing 4) so i can use it in the run method without using inner classes? Thank you hansa Reformulation of Question: How to make the send-method of inner class MessageSender make accessible in ClassThatDoSomething. Example-Code: public class Example extends HttpServlet implements CometProcessor { private MessageSender messageSender = null; @Override public void init() throws ServletException { // starts thread MessageSender } public event(CometEvent) { // Object of ClassThatDoSomething gets created started } private class ClassThatDoSomething { public void start() { Runnable runnable = new Runnable() { public void run(){ messageSender.send(message); } Thread thread = new Thread(runnable); thread.start(); } } private class MessageSender implements Runnable { public void send(String message) { //... } public void run() { //...} } }

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• Porting C++-code from Windows to Unix: systemcalls colliding with name of functions

  - by marvin2k

  Hi I'm porting some crufty C++ Windows-code to Linux, which uses functions called "open" and "close" inside every class... Very bad style, or? Luckily that wasn't a problem in windows, since their systemcalls are named different. When I try to call the systemcalls open() or close() I'm getting some compiler error about "no matching function for call for class:open()". I can't rename all our functions named "class::open" and "class::close" in the whole code, and I have to use open() and close() since I'm working with serial ports. So my question is: How can I tell the compiler, which open I mean? How can I escape or hide the namespace of a class in C++?

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• Does importing of packages change visibility of classes?

  - by Roman

  I jsut learned that A class may be declared with the modifier public, in which case that class is visible to all classes everywhere. If a class has no modifier (the default, also known as package-private), it is visible only within its own package. This is a clear statement. But this information interfere with my understanding of importing of packages (which easily can be wrong). I thought that importing a package I make classes from the imported package visible to the importing class. So, how does it work? Are public classes visible to all classes everywhere under condition that the package containing the public class is imported? Or there is not such a condition? What about the package-private classes? They are invisible no mater if the containing package was imported or not? ADDED: It seems to me that I got 2 answers which are marked as good (up-voted) and which contradict eachother.

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• Setting a preferred item of a many-to-one in Django

  - by Mike DeSimone

  I'm trying to create a Django model that handles the following: An Item can have several Names. One of the Names for an Item is its primary Name, i.e. the Name displayed given an Item. (The model names were changed to protect the innocent.) The models.py I've got looks like: class Item(models.Model): primaryName = models.OneToOneField("Name", verbose_name="Primary Name", related_name="_unused") def __unicode__(self): return self.primaryName.name class Name(models.Model): item = models.ForeignKey(Item) name = models.CharField(max_length=32, unique=True) def __unicode__(self): return self.name class Meta: ordering = [ 'name' ] The admin.py looks like: class NameInline(admin.TabularInline): model = Name class ItemAdmin(admin.ModelAdmin): inlines = [ NameInline ] admin.site.register(Item, ItemAdmin) It looks like the database schema is working fine, but I'm having trouble with the admin, so I'm not sure of anything at this point. My main questions are: How do I explain to the admin that primaryName needs to be one of the Names of the item being edited? Is there a way to automatically set primaryName to the first Name found, if primaryName is not set, since I'm using inline admin for the names?

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• C++ function-pointer and inheritance

  - by pingvinus

  In parent class I have function, that operates under an array of functions, declared in child-class, number of functions for every child-class may vary. But since every function uses some object-variables, I can't declare them as static. I've try to do something like this: class A { public: typedef int (A::*func)(); func * fs; void f() { /*call functions from this->fs*/ } }; class B : public A { public: int smth; B(int smth) { this->smth = smth; this->fs = new func[1]; fs[0] = &B::f; } int f() { return smth + 1; } }; But, obviously it doesn't work. Any suggestions?

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• Design question - loading info from DB

  - by eriks

  I need to build a class that will represent a row in some table in DB (lets say the table is 'Subscriber' and so is the class). I can have the class Subscriber which constructor receives the Objectkey of subscriber, retrieves info from DB and initializes its members. I add another class - SubscriberLoader which have a static method 'LoadSubscriber'. This method will receive the subscriber objectkey, retrieve info from DB, crate a Subscriber object and initialize its members. Subscriber constructor will be private and SubscirberLoader will be friend class of Subscriber - this way, client could build a Subscriber only using the loader. which of the two in better? any other suggestions?

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• Why my :hover aren't working?

  - by user1628488

  I have am nav, and when i hover some elements, the submenu should be displayed 'block', but this dont work. See <!doctype html> <html lang="pt-br"> <head> <meta charset="utf-8" /> <meta name="robots" content="noindex, nofollow" /> <meta name="generator" content="Notepad++" /> <meta name="author" content="Erick Ribeiro" /> <meta http-equiv="refresh" content="60" /> <title>Mozilla Firefox</title> <style type="text/css"> *{ font-family: calibri; } #menu { float: left; } .submenu { margin-top: 26px; padding: 10px; border: solid 1px rgb(224, 224, 224); background: rgb(254, 254, 254); color: rgb(0, 128, 224); border-radius: 0 0 4px 4px; } #menuHome:hover ~ #submenuControle { display: block; opacity: 0; color: red; } #submenuHome { display: none; opacity: 0; } #submenuControle { display: block; opacity: 1; } #submenuGestão { display: none; opacity: 0; } #submenuRL { display: none; opacity: 0; } #submenuSI { display: none; opacity: 0; } ul { float: left; list-style-type: none; padding: 0; margin: 0; } li { display: inline; float:left; } .primeiroItem { border: solid rgb(224, 224, 224); border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 1px; border-radius: 4px 0 0 4px; } .naoPrimeiroItem { border: solid rgb(224, 224, 224); border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 0; } .ultimoItem { border: solid rgb(224, 224, 224); border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 0; border-radius: 0 4px 4px 0; } a { text-decoration:none; padding: 8px; border: solid 1px; color: rgb(0, 0, 0); background: rgb(240,240, 240); } a:visited { color: rgb(0, 0, 0); } </style> <script type="text/javascript"> </script> </head> <body> <nav id="menu"> <ul> <li><a id="menuHome" class="primeiroItem" href="#">Home</a></li> <li><a id="menuControle" class="naoPrimeiroItem" href="#">Controle</a></li> <li><a id="menuGestao" class="naoPrimeiroItem" href="#">Gestão</a></li> <li><a id="menuRL" class="naoPrimeiroItem" href="#">Relatórios e Listas</a></li> <li><a id="menuSI" class="ultimoItem" href="#">Sistema Informação</a></li> </ul> <div id="submenuHome" class="submenu"> </div> <div id="submenuControle" class="submenu"> BSC Comunicação Treinamento Documentos Controle de Acesso </div> <div id="submenuGestão" class="submenu"> ASV Treinamento Suprimentos Chamados</div> <div id="submenuRL" class="submenu"> Listas Relatórios </div> <div id="submenuSI" class="submenu"> </div> </nav> </body> </html>

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• Java cannot find symbol enum

  - by JDelage

  Hi, I'm modeling a chess game on Java, and I'm having some problem. Here's what the code looks like (the relevant parts): Enum class Couleur.java: public enum Couleur {BLANC, NOIR} Piece.java: public abstract class Piece { (...) public Piece(Couleur couleurParam){ this.couleurPiece = couleurParam; } (...) } And finally Tour.java: public class Tour extends Piece { (...) public Tour(Couleur couleurParam){ super(couleurParam); } (...) } All the .java files are in the same folder. Yet at compile I get a "cannot find symbol symbol : variable NOIR location: class Plateau" (Plateau is the class that instantiates Tour.) Can anyone help me figure out what's wrong here? Many thanks, JDelage

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• What's the preferred way to use helper methods in Ruby?

  - by DR

  Disclaimer: Although I'm asking in context of a Rails application, I'm not talking about Rails helpers (i.e. view helpers) Let's say I have a helper method/function: def dispatch_job(job = {}) #Do something end Now I want to use this from several places (mostly controllers, but also a few BackgrounDRb workers) What's the preferred way to do this? I can think of two possibilities: 1. Use a class and make the helper a static method: class MyHelper def self.dispatch_job(job = {}) end end class MyWorker def run MyHelper.dispatch_job(...) end end 2. Use a module and include the method into whatever class I need this functionality module MyHelper def self.dispatch_job(job = {}) end end class MyWorker include MyHelper def run dispatch_job(...) end end 3. Other possibilities I don't know yet ... The first one is more Java-like, but I'm not sure if the second one is really an appropriate use of Ruby's modules.

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• C++: retrieve map values and insert into second map

  - by donalmg

  Hi, I have one map within one header file class: class One { // code typedef map<string, int> MapStrToInt inline MapStrToInt& GetDetails(unsigned long index) { return pData[index]; } // populate pData.... private: MapStrToInt *pData; }; And a second class which implements another map and wants to get the first 10 details from the class One's map. class Two { // code One::MapStrToInt pDataTen; int function1() { for (int i =0; i < 10; i ++) { One::MapStrToInt * pMap = &(One::GetDetails(i)); pDataTen.insert(pair<string, int>(pMap->first,pMap->second)); } } When I compile this, it states that pMap: has no member named 'first' has no member named 'second' Any suggestions? Thanks..

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• Visual-C++ Linker Error

  - by LordByron

  I have a class called MODEL in which public static int theMaxFrames resides. The class is defined in its own header file. theMaxFrames is accessed by a class within the MODEL class and by one function, void set_up(), which is also in the MODEL class. The Render.cpp source file contains a function which calls a function in the Direct3D.cpp source file which in turn calls the set_up() function through a MODEL object. This is the only connection between these two source files and theMaxFrames. When I try to compile my code I get the following error messages: 1Direct3D.obj : error LNK2001: unresolved external symbol "public: static int MODEL::theMaxFrames" (?theMaxFrames@MODEL@@2HA) 1Render.obj : error LNK2001: unresolved external symbol "public: static int MODEL::theMaxFrames" (?theMaxFrames@MODEL@@2HA) 1C:\Users\Byron\Documents\Visual Studio 2008\Projects\xFileViewer\Debug\xFileViewer.exe : fatal error LNK1120: 1 unresolved externals

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