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• How to have variables with dynamic data types in Java?

  - by Nazgulled

  Hi, I need to have a UserProfile class that it's just that, a user profile. This user profile has some vital user data of course, but it also needs to have lists of messages sent from the user friends. I need to save these messages in LinkedList, ArrayList, HashMap and TreeMap. But only one at a time and not duplicate the message for each data structure. Basically, something like a dynamic variable type where I could pick the data type for the messages. Is this, somehow, possible in Java? Or my best approach is something like this? I mean, have 2 different classes (for the user profile), one where I host the messages as Map<K,V> (and then I use HashMap and TreeMap where appropriately) and another class where I host them as List<E> (and then I use LinkedList and ArrayList where appropriately). And probably use a super class for the UserProfile so I don't have to duplicate variables and methods for fields like data, age, address, etc... Any thoughts?

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• Generics in a bidirectional association

  - by Verhoevenv

  Let's say I have two classes A and B, with B a subtype of A. This is only part of a richer type hierarchy, obviously, but I don't think that's relevant. Assume A is the root of the hierarchy. There is a collection class C that keeps track of a list of A's. However, I want to make C generic, so that it is possible to make an instance that only keeps B's and won't accept A's. class A(val c: C[A]) { c.addEntry(this) } class B(c: C[A]) extends A(c) class C[T <: A]{ val entries = new ArrayBuffer[T]() def addEntry(e: T) { entries += e } } object Generic { def main(args : Array[String]) { val c = new C[B]() new B(c) } } The code above obviously give the error 'type mismatch: found C[B], required C[A]' on the new B(c) line. I'm not sure how this can be fixed. It's not possible to make C covariant in T (like C[+T <: A]) because the ArrayBuffer is non-variantly typed in T. It's not possible to make the constructor of B require a C[B] because C can't be covariant. Am I barking up the wrong tree here? I'm a complete Scala newbie, so any ideas and tips might be helpful. Thank you! EDIT: Basically, what I'd like to have is that the compiler accepts both val c = new C[B]() new B(c) and val c = new C[A]() new B(c) but would reject val c = new C[B]() new A(c) It's probably possible to relax the typing of the ArrayBuffer in C to be A instead of T, and thus in the addEntry method as well, if that helps.

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• When inheriting a control in Silverlight, how to find out if its template has been applied?

  - by herzmeister der welten

  When inheriting a control in Silverlight, how do I find out if its template has already been applied? I.e., can I reliably get rid of my cumbersome _hasTemplateBeenApplied field? public class AwesomeControl : Control { private bool _hasTemplateBeenApplied = false; public override void OnApplyTemplate() { base.OnApplyTemplate(); this._hasTemplateBeenApplied = true; // Stuff } private bool DoStuff() { if (this._hasTemplateBeenApplied) { // Do Stuff } } }

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• Calling an Overridden Method from a Parent-Class Constructor

  - by Vaibhav Bajpai

  I tried calling an overridden method from a constructor of a parent class and noticed different behavior across languages. C++ - echoes A.foo() class A{ public: A(){foo();} virtual void foo(){cout<<"A.foo()";} }; class B : public A{ public: B(){} void foo(){cout<<"B.foo()";} }; int main(){ B *b = new B(); } Java - echoes B.foo() class A{ public A(){foo();} public void foo(){System.out.println("A.foo()");} } class B extends A{ public void foo(){System.out.println("B.foo()");} } class Demo{ public static void main(String args[]){ B b = new B(); } } C# - echoes B.foo() class A{ public A(){foo();} public virtual void foo(){Console.WriteLine("A.foo()");} } class B : A{ public override void foo(){Console.WriteLine("B.foo()");} } class MainClass { public static void Main (string[] args) { B b = new B(); } } I realize that in C++ objects are created from top-most parent going down the hierarchy, so when the constructor calls the overridden method, B does not even exist, so it calls the A' version of the method. However, I am not sure why I am getting different behavior in Java and C#.

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• C++ Problem: Class Promotion using derived class

  - by Michael Fitzpatrick

  I have a class for Float32 that is derived from Float32_base class Float32_base { public: // Constructors Float32_base(float x) : value(x) {}; Float32_base(void) : value(0) {}; operator float32(void) {return value;}; Float32_base operator =(float x) {value = x; return *this;}; Float32_base operator +(float x) const { return value + x;}; protected: float value; } class Float32 : public Float32_base { public: float Tad() { return value + .01; } } int main() { Float32 x, y, z; x = 1; y = 2; // WILL NOT COMPILE! z = (x + y).Tad(); // COMPILES OK z = ((Float32)(x + y)).Tad(); } The issue is that the + operator returns a Float32_base and Tad() is not in that class. But 'x' and 'y' are Float32's. Is there a way that I can get the code in the first line to compile without having to resort to a typecast like I did on the next line?

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• Java - How to pass a Generic parameter as Class<T> to a constructor

  - by Joe Almore

  I have a problem here that still cannot solve, the thing is I have this abstract class: public abstract class AbstractBean<T> { private Class<T> entityClass; public AbstractBean(Class<T> entityClass) { this.entityClass = entityClass; }... Now I have another class that inherits this abstract: @Stateless @LocalBean public class BasicUserBean<T extends BasicUser> extends AbstractBean<T> { private Class<T> user; public BasicUserBean() { super(user); // Error: cannot reference user before supertype contructor has been called. } My question is how can I make this to work?, I am trying to make the class BasicUserBean inheritable, so if I have class PersonBean which inherits BasicUserBean then I could set in the Generic the entity Person which also inherits the entity BasicUser. And it will end up being: @Stateless @LocalBean public class PersonBean extends BasicUserBean<Person> { public PersonBean() { super(Person.class); } ... I just want to inherit the basic functionality from BasicUserBean to all descendants, so I do not have to repeat the same code among all descendants. Thanks!.

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• Get derived class type from a base's class static method

  - by Marco Bettiolo

  Hi, i would like to get the type of the derived class from a static method of its base class. How can this be accomplished? Thanks! class BaseClass { static void Ping () { Type t = this.GetType(); // should be DerivedClass, but it is not possible with a static method } } class DerivedClass : BaseClass {} // somewhere in the code DerivedClass.Ping();

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• Extending a Java Swing class in Clojure

  - by mikera

  I'm trying to extend a Java Swing component in Clojure, i.e. I want to extend a javax.swing.JComponent and add some custom methods implemented in pure Clojure in addition to all the standard inherited methods. I've tried using "proxy" which works great if I just want a single instance (in the same way as an anonymous inner class). However I'd really like a named class so that I can generate an arbitrary number of instances. What's the recommended way of doing this?

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• C++ parent class alignment

  - by aaa

  hello. Is it possible to specify alignment of parent class? for example something like (which does not compiled): template<size_t n> class Vector : public boost::array<double,n> __attribute__ ((aligned(16))) { thanks

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• Inheriting a Base Form but Paste/Cut Commands Not Captured

  - by ohu812

  I created a base form that has a specific size and an icon as a base for all forms created in my project (to be consistent in looks). The problem is, for some reason if I add a Text box to the Child form, I can no longer execute shortcuts like Copy (CTRL+C) etc into the Textbox. What should I do to handle this OTHER THAN writing code to capture those on the KeyUp control? This is also the case for RichTextBox control as well. Thanks

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• Passing derived objects in a constructure

  - by Clarence Klopfstein

  This is a bit of a convoluted question, hopefully I can make it clear. I am finding that this may not be possible, but am trying to see if anybody has a solution. I have four classes, two are core classes and two are those core classes extended: extUser Extends coreUser extSecurity Extends coreSecurity In the constructor for coreUser you have this: public coreUser(string id, ref coreSecurity cs) When trying to extend coreUser you would have this: public extUser(string id ref extSecurity es) : base(id, ref es) This fails because es is of type, extSecurity and the base class expects a type of coreSecurity. I've not found anyway to cast this to allow for me to override this base class in C#. In VB it works just fine. Ideas?

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• Force calling the derived class implementation within a generic function in C#?

  - by Adam Hardy

  Ok so I'm currently working with a set of classes that I don't have control over in some pretty generic functions using these objects. Instead of writing literally tens of functions that essentially do the same thing for each class I decided to use a generic function instead. Now the classes I'm dealing with are a little weird in that the derived classes share many of the same properties but the base class that they are derived from doesn't. One such property example is .Parent which exists on a huge number of derived classes but not on the base class and it is this property that I need to use. For ease of understanding I've created a small example as follows: class StandardBaseClass {} // These are simulating the SMO objects class StandardDerivedClass : StandardBaseClass { public object Parent { get; set; } } static class Extensions { public static object GetParent(this StandardDerivedClass sdc) { return sdc.Parent; } public static object GetParent(this StandardBaseClass sbc) { throw new NotImplementedException("StandardBaseClass does not contain a property Parent"); } // This is the Generic function I'm trying to write and need the Parent property. public static void DoSomething<T>(T foo) where T : StandardBaseClass { object Parent = ((T)foo).GetParent(); } } In the above example calling DoSomething() will throw the NotImplemented Exception in the base class's implementation of GetParent(), even though I'm forcing the cast to T which is a StandardDerivedClass. This is contrary to other casting behaviour where by downcasting will force the use of the base class's implementation. I see this behaviour as a bug. Has anyone else out there encountered this?

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• C# - are private members inherited?

  - by Petr

  Hi, Just seen one tutorial saying that: Class Dog { private string Name; } Class SuperDog:Dog { private string Mood; } Then there was an UML displaying that SuperDog will inherit Name as well. I have tried but to me it seems that only public members are inherited. At least I could not access Name unless it was declared as public. Thanks

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• inheritence in c#

  - by scatman

  i am trying to create a custom (TreeView) control by inheriting from (RadTreeView) control by doing so: public class CustTreeView : RadTreeView but not all methods where inherited!!. for example: i can do: RadTreeView r = new RadTreeView(); r.LoadContentFile("Sample.xml"); but not: CustTreeView r = new CustTreeView (); r.LoadContentFile("Sample.xml"); so LoadContentFile is a method in RadTreeView but not in CustTreeView!!any explanation?

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• Setting the type of a field in a superclass from a subclass (Java)

  - by Ibolit

  Hi. I am writing a project on Google App Engine, within it I have a number of abstract classes that I hope I will be able to use in my future projects, and a number of concrete classes inheriting from them. Among other abstract classes I have an abstract servlet that does user management, and I hava an abstract user. The AbstractUser has all the necessary fields and methods for storing it in the datastore and telling whether the user is registered with my service or not. It does not implement any project specific functionality. The abstract servlet that manages users, refers only to the methods declared in the AbstractUser class, which allows it to generate links for logging in, logging out and registering (for unregistered users). In order to implement the project-specific user functionality I need to subclass the Abstract user. The servlets I use in my project are all indirect descendants from that abstract user management servlet, and the user is a protected field in it, so the descendant servlets can use it as their own field. However, whenever i want to access any project specific method of the concrete user, i need to cast it to that type. i.e. (abstract user managing servlet) ... AbstractUser user = getUser(); ... abstract protected AbstractUser getUser(); (project-specific abstract servlet) @Override protected AbstractUser getUser() { return MyUserFactory.getUser(); } any other project specific servlet: int a = ((ConcreteUser) user).getA(); Well, what i'd like to do is to somehow make the type of “user” in the superclass depend on something in the project-specific abstract class. Is it at all possible? And i don't want to move all the user-management stuff into a project-specific layer, for i would like to have it for my future projects already written :) Thank you for your help.

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• C++ enforce conditions on inherited classes

  - by user231536

  I would like to define an abstract base class X and enforce the following: a) every concrete class Y that inherits from X define a constructor Y(int x) b) it should be possible to test whether two Y objects are equal. For a, one not very good solution is to put a pure virtual fromInt method in X which concrete class will have to define. But I cannot enforce construction. For b), I cannot seem to use a pure virtual method in X bool operator == (const X& other) const =0; because in overridden classes this remains undefined. It is not enough to define bool operator == (const Y& other) const { //stuff} because the types don't match. How do I solve these problems?

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• When calling a static method on parent class, can the parent class deduce the type on the child (C#)

  - by Matt

  Suppose we have 2 classes, Child, and the class from which it inherits, Parent. class Parent { public static void MyFunction(){} } class Child : Parent { } Is it possible to determine in the parent class how the method was called? Because we can call it two ways: Parent.MyFunction(); Child.MyFunction(); My current approach was trying to use: MethodInfo.GetCurrentMethod().ReflectedType; // and MethodInfo.GetCurrentMethod().DeclaringType; But both appear to return the Parent type. If you are wondering what, exactly I am trying to accomplish (and why I am violating the basic OOP rule that the parent shouldn't have to know anything about the child), the short of it is this (let me know if you want the long version): I have a Model structure representing some of our data that persists to the database. All of these models inherit from an abstract Parent. This parent implements a couple of events, such as SaveEvent, DeleteEvent, etc. We want to be able to subscribe to events specific to the type. So, even though the event is in the parent, I want to be able to do: Child.SaveEvent += new EventHandler((sender, args) => {}); I have everything in place, where the event is actually backed by a dictionary of event handlers, hashed by type. The last thing I need to get working is correctly detecting the Child type, when doing Child.SaveEvent. I know I can implement the event in each child class (even forcing it through use of abstract), but it would be nice to keep it all in the parent, which is the class actually firing the events (since it implements the common save/delete/change functionality).

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• PHP inheriting/extending a particular instance of an Object

  - by delta9

  Is there any way to force PHP to extend an existing/particular (and for that matter, already instantiated) instance of an object? This imaginary code should explain what I am wondering: class Base { public $var; function __construct($var){ $this->var = $name; } } class Extender extends Base { function __construct($parent) { parent = $parent; } } $base = new Base('yay!'); $extender = new Extender($base); echo 'Extended base var value: '.$extender->var.'<br/>'; Output (would be): Extended base var value: yay! To be clear, I am wanting to instantiate an object that extends a PARTICULAR INSTANCE of another object, one that has already been instantiated. I am aware that I can pass a reference to an object to another object (via it's constructor function) and then add it as a property of the receiving object, I'm wondering if there is a real way to do this?

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• Friendness and derived class

  - by ereOn

  Hi, Let's say I have the following class hierarchy: class Base { protected: virtual void foo() = 0; friend class Other; }; class Derived : public Base { protected: void foo() { /* Some implementation */ }; }; class Other { public: void bar() { Derived* a = new Derived(); a->foo(); // Compiler error: foo() is protected within this context }; }; I guess I could change it too a->Base::foo() but since foo() is pure virtual in the Base class, the call will result in calling Derived::foo() anyway. However, the compiler seems to refuse a->foo(). I guess it is logical, but I can't really understand why. Am I missing something ? Can't (shouldn't) it handle this special case ? Thank you.

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• How to override "inherited" z-indexes?

  - by Earlz

  I am needing to override the notion of inherited z-indexes. For instance in this code <style> div{ background-color:white; top: 0px; bottom: 0px; left: 0px; right: 0px; } </style> <div style="position: fixed; z-index: 2;"> div 1 <div style="position: fixed; z-index: 3;"> div 2 </div> </div> <div style="position: fixed; z-index: 2;"> div 3 </div> http://jsbin.com/epoqo3/3 I want for div 2 to be displayed, but instead div 3 is displayed. How can I change this behavior without changing my structure.

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• Add Method to Built In Class

  - by Evorlor

  I am pretty sure this is not doable, but I will go ahead and cross my fingers and ask. I am trying to add a method to a built in class. I want this method to be callable by all of the built in class's subclasses. Specifically: I have a JButton, a JTextPane, and other JComponents. I want to be able to pass in a JDom Element instead of a Rectangle to setBounds(). My current solution is to extend each JComponent subclass with the desired methods, but that is a LOT of duplicate code. Is there a way I can write the following method just one time, and have it callable on all JComponent objects? Or is it required that I extend each subclass individually, and copy and paste the method below? public void setBounds(Element element) { this.setBounds(Integer.parseInt(element.getAttribute( "x").toString()), Integer.parseInt(element .getAttribute("y").toString()), Integer .parseInt(element.getAttribute("width").toString()), Integer.parseInt(element.getAttribute("height") .toString())); }

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• C++ - Error: expected unqualified-id before ‘using’

  - by Francisco P.

  Hello, everyone. I am having some trouble on a project I'm working on. Here's the header file for the calor class: #ifndef _CALOR_ #define _CALOR_ #include "gradiente.h" using namespace std; class Calor : public Gradiente { public: Calor(); Calor(int a); ~Calor(); int getTemp(); int getMinTemp(); void setTemp(int a); void setMinTemp(int a); void mostraSensor(); }; #endif When I try to compile it: calor.h|6|error: expected unqualified-id before ‘using’| Why does this happen? I've been searching online and learned this error occurs mostly due to corrupted included files. Makes no sense to me, though. This class inherits from gradiente: #ifndef _GRADIENTE_ #define _GRADIENTE_ #include "sensor.h" using namespace std; class Gradiente : public Sensor { protected: int vActual, vMin; public: Gradiente(); ~Gradiente(); } #endif Which in turn inherits from sensor #ifndef _SENSOR_ #define _SENSOR_ #include <iostream> #include <fstream> #include <string> #include "definicoes.h" using namespace std; class Sensor { protected: int tipo; int IDsensor; bool estadoAlerta; bool estadoActivo; static int numSensores; public: Sensor(/*PARAMETROS*/); Sensor(ifstream &); ~Sensor(); int getIDsensor(); bool getEstadoAlerta(); bool getEstadoActivo(); void setEstadoAlerta(int a); void setEstadoActivo(int a); virtual void guardaSensor(ofstream &); virtual void mostraSensor(); // FUNÇÃO COMUM /* virtual int funcaoComum() = 0; virtual int funcaoComum(){return 0;};*/ }; #endif For completeness' sake, here's definicoes.h #ifndef _DEFINICOES_ #define _DEFINICOES_ const unsigned int SENSOR_MOVIMENTO = 0; const unsigned int SENSOR_SOM = 1; const unsigned int SENSOR_PRESSAO = 2; const unsigned int SENSOR_CALOR = 3; const unsigned int SENSOR_CONTACTO = 4; const unsigned int MIN_MOVIMENTO = 10; const unsigned int MIN_SOM = 10; const unsigned int MIN_PRESSAO = 10; const unsigned int MIN_CALOR = 35; #endif Any help'd be much appreciated. Thank you for your time. Thanks for your time!

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• Problem with inherited classes in C#

  - by Unniloct

  I have a class called "Entity," with two child classes: "Creature" and "Item." (I'm making a game.) Creature has two functions called "Attack," one for attacking Creatures, and one for attacking Items. So far, everything works well. Now I'm working on the shooting bit, so I have a function called SelectTarget(). It takes all of the Entities (both Creatures and Items) in the player's view that the player can shoot and lets the player choose one. So here lies the problem: SelectTarget() returns an Entity, but I need some code to figure out whether that Entity is a Creature or an Item, and process it appropriately. Since this question looks kind of empty without any code, and I'm not 100% sure my explanation is good enough, here's where I'm at: if (Input.Check(Key.Fire)) { Entity target = Game.State.SelectTarget.Run(); this.Draw(); if (target != null) { //Player.Attack(target); // This won't work, because I have: // Player.Attack((Creature)Target) // Player.Attack((Item)Target) // but nothing for Entity, the parent class to Creature and Item. return true; } } (If the way the game is laid out seems weird, it's a roguelike.)

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• C# Why does code compile fine when there is an ambiguous virtual method?

  - by Jimbo

  I have a class (Class B) that inherits another class (Class A) that contains virtual methods. Mistakenly, I omitted the override keyword when declaring a (supposed to be) overriding method in Class B. Class A public class ClassA{ public virtual void TestMethod(){ } } Class B public class ClassB : ClassA{ public void TestMethod(){ } } The code compiled without a problem. Can anyone explain why?

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• Create object of unknown class (two inherited classes)

  - by Paul

  I've got the following classes: class A { void commonFunction() = 0; } class Aa: public A { //Some stuff... } class Ab: public A { //Some stuff... } Depending on user input I want to create an object of either Aa or Ab. My imidiate thought was this: A object; if (/*Test*/) { Aa object; } else { Ab object; } But the compiler gives me: error: cannot declare variable ‘object’ to be of abstract type ‘A’ because the following virtual functions are pure within ‘A’: //The functions... Is there a good way to solve this?

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