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  • Can I make a derived class inherit a derived member from its base class in Java?

    - by Eric
    I have code that looks like this: public class A { public void doStuff() { System.out.print("Stuff successfully done"); } } public class B extends A { public void doStuff() { System.out.print("Stuff successfully done, but in a different way"); } public void doMoreStuff() { System.out.print("More advanced stuff successully done"); } } public class AWrapper { public A member; public AWrapper(A member) { this.member = member; } public void doStuffWithMember() { a.doStuff(); } } public class BWrapper extends AWrapper { public B member; public BWrapper(B member) { super(member); //Pointer to member stored in two places: this.member = member; //Not great if one changes, but the other does not } public void doStuffWithMember() { member.doMoreStuff(); } } However, there is a problem with this code. I'm storing a reference to the member in two places, but if one changes and the other does not, there could be trouble. I know that in Java, an inherited method can narrow down its return type (and perhaps arguments, but I'm not certain) to a derived class. Is the same true of fields?

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  • Accessing methods of an object put inside a class

    - by Klaus
    Hello, A class A possesses an instance c of a class C. Another class B has to modify c through C::setBlah(); method. Is it bad to create an accessor C getC(); in A and then use A.getC().setBlah() ? Or should I create a method A::setBlah(); that would call C::setBlah(); ? Isn't it annoying if there are several methods like that ?

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  • Setting class properties quickly

    - by uzay95
    class UserClass{ #region Class properties which are binding from DB . . . #endregion #region Constructor Methods public UserClass(int _iUser_id) { // of course this is wrong but how can i quickly set properties // which are coming from DB by extension method over context class? this = DAO.context.GetById<UserClass>(_iUser_id); } #endregion }

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  • How to access constant defined in child class from parent class functions?

    - by kavoir.com
    I saw this example from php.net: <?php class MyClass { const MY_CONST = "yonder"; public function __construct() { $c = get_class( $this ); echo $c::MY_CONST; } } class ChildClass extends MyClass { const MY_CONST = "bar"; } $x = new ChildClass(); // prints 'bar' $y = new MyClass(); // prints 'yonder' ?> But $c::MY_CONST is only recognized in version 5.3.0 or later. The class I'm writing may be distributed a lot. Basically, I have defined a constant in ChildClass and one of the functions in MyClass (father class) needs to use the constant. Any idea?

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  • singledispatch in class, how to dispatch self type

    - by yanxinyou
    Using python3.4. Here I want use singledispatch to dispatch different type in __mul__ method . The code like this : class Vector(object): ## some code not paste @functools.singledispatch def __mul__(self, other): raise NotImplementedError("can't mul these type") @__mul__.register(int) @__mul__.register(object) # Becasue can't use Vector , I have to use object def _(self, other): result = Vector(len(self)) # start with vector of zeros for j in range(len(self)): result[j] = self[j]*other return result @__mul__.register(Vector) # how can I use the self't type @__mul__.register(object) # def _(self, other): pass # need impl As you can see the code , I want support Vector*Vertor , This has Name error Traceback (most recent call last): File "p_algorithms\vector.py", line 6, in <module> class Vector(object): File "p_algorithms\vector.py", line 84, in Vector @__mul__.register(Vector) # how can I use the self't type NameError: name 'Vector' is not defined The question may be How Can I use class Name a Type in the class's method ? I know c++ have font class statement . How python solve my problem ? And it is strange to see result = Vector(len(self)) where the Vector can be used in method body .

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  • Class templating std::set key types

    - by TomFLuff
    I have a class to evaluate set algebra but wish to template it. At the minute it looks a bit like this set.h: template<typename T> class SetEvaluation { public: SetEvaluation<T>(); std::set<T> evaluate(std::string in_expression); } set.cpp template<typename T> std::set<T> SetEvaluation<T>::evaluate(std::string expression) { std::set<T> result; etc etc... } But i'm getting undefined reference errors when compiling. Is it possible to declare the return type as std::set<T> and then pass std::string as the class template param. There are no errors in the class but only when I try to instantiate SetEvaluation<std::string> Can anyone shed light on this problem? thanks

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  • AS3 - Can I know if a class implements an interface (or is a subclass of another class) ?

    - by lk
    With this code function someFunction(classParam:Class):Boolean { // how to know if classParam implements some interface? } i.e. Comparing classParam with IEventDispatcher interface: someFunction(EventDispatcher) // returns true someFunction(Object) // returns false I know it can't be done with is operator. But, is there a way to do it? Is there a way to know if a class implements some interface? (or is a subclass of another class?)

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  • Access property from include inside a class method in PHP

    - by Jojo
    How do you make a class property available to the other included file inside the same class' method? // file A.php class A { private $var = 1; public function go() { include('another.php'); } } in another file: // this is another.php file // how can I access class A->var? echo $var; // this can't be right Is this possible given the scope. If var is an array then we can use extract but if var is not, we can wrap it in an array. Is there a better way? Thanks!

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  • Rails: i have a class method and i want to modify something of the instance

    - by Totty
    Rails: i have a class method and i want to modify something of the instance something like this: class Test < Main template :box def test # here I want to access the template name, that is box end end class Main def initialize end def self.template(name) # here I have to save somehow the template name # remember is not an instance. end end that is similar to the model classes: # in the model has_many :projects How do I do it?

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  • Getting many files from a SharePoint Document Library the easy way

    - by Stacy Vicknair
    As an individual who does not use Internet Explorer as their primary browser, there is a great feature that you may never notice that allows you to easily copy files to and from a document library: the Open in Windows Explorer link. In browsers such as Chrome or Firefox this link may not appear. I know this isn’t a major groundbreaking feature, but it’s really easy to overlook and it’s worth knowing about, especially when you need to create a local copy of a full document library. In this quick blog we’ll go over how to access this feature in both SharePoint 2007 and 2010. First, make sure you are in Internet Explorer. These options may not show in other browsers. In SharePoint 2007, browse to the document library you would like to access then select Actions > Open with Windows Explorer. In SharePoint 2010, browse to the document library you would like to access then select Library Tools > Library > Open with Explorer from the ribbon.

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  • Can You Have "Empty" Abstract/Classes?

    - by ShrimpCrackers
    Of course you can, I'm just wondering if it's rational to design in such a way. I'm making a breakout clone and was doing some class design. I wanted to use inheritance, even though I don't have to, to apply what I've learned in C++. I was thinking about class design and came up with something like this: GameObject - base class (consists of data members like x and y offsets, and a vector of SDL_Surface* MovableObject : GameObject - abstract class + derived class of GameObject (one method void move() = 0; ) NonMovableObject : GameObject - empty class...no methods or data members other than constructor and destructor(at least for now?). Later I was planning to derive a class from NonMovableObject, like Tileset : NonMovableObject. I was just wondering if "empty" abstract classes or just empty classes are often used...I notice that the way I'm doing this, I'm just creating the class NonMovableObject just for sake of categorization. I know I'm overthinking things just to make a breakout clone, but my focus is less on the game and more on using inheritance and designing some sort of game framework.

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  • http-equiv=content-language alternative - the way of specifying document language

    - by tugberk
    Lots of web sites uses following meta tag to specify the default language of the document: <meta http-equiv="content-language" content="es-ES"> When I go to w3c site: http://www.w3.org/TR/2011/WD-html-markup-20110113/meta.http-equiv.content-language.html#meta.http-equiv.content-language I get this: Using the meta element to specify the document-wide default language is obsolete. Consider specifying the language on the root element instead. What is the way of specifying document language now?

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  • Should you document everything or just most?

    - by TheLQ
    It seems a bit of a controversial subject to document everything, including the "JavaBean" syntax of getters and setters for fields: People say its needlessly long and repetitive breaking DRY (don't repeat yourself), that the naming convention should explain everything, and it clutters code/documentation. Sometimes those arguments work. But other times, you end up with this: Above is common to open source projects that do boldly follow those principles. Your left with entirely useless documentation. That doesn't explain anything about whats going on underneath, the possible effects, or even what the expected value is (could it be null or never null? I don't know, the Javadoc doesn't tell me). So when should I document? Do I document everything even if it occasionally clutters code? Or do I document nothing since in my eyes its "obvious"?

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  • What is the recommended MongoDB schema for this quiz-engine scenario?

    - by hughesdan
    I'm working on a quiz engine for learning a foreign language. The engine shows users four images simultaneously and then plays an audio file. The user has to match the audio to the correct image. Below is my MongoDB document structure. Each document consists of an image file reference and an array of references to audio files that match that image. To generate a quiz instance I select four documents at random, show the images and then play one audio file from the four documents at random. The next step in my application development is to decide on the best document schema for storing user guesses. There are several requirements to consider: I need to be able to report statistics at a user level. For example, total correct answers, total guesses, mean accuracy, etc) I need to be able to query images based on the user's learning progress. For example, select 4 documents where guess count is 10 and accuracy is <=0.50. The schema needs to be optimized for fast quiz generation. The schema must not cause future scaling issues vis a vis document size. Assume 1mm users who make an average of 1000 guesses. Given all of this as background information, what would be the recommended schema? For example, would you store each guess in the Image document or perhaps in a User document (not shown) or a new document collection created for logging guesses? Would you recommend logging the raw guess data or would you pre-compute statistics by incrementing counters within the relevant document? Schema for Image Collection: _id "505bcc7a45c978be24000005" date 2012-09-21 02:10:02 UTC imageFileName "BD3E134A-C7B3-4405-9004-ED573DF477FE-29879-0000395CF1091601" random 0.26997075392864645 user "2A8761E4-C13A-470E-A759-91432D61B6AF-25982-0000352D853511AF" audioFiles [ 0 { audioFileName "C3669719-9F0A-4EB5-A791-2C00486665ED-30305-000039A3FDA7DCD2" user "2A8761E4-C13A-470E-A759-91432D61B6AF-25982-0000352D853511AF" audioLanguage "English" date 2012-09-22 01:15:04 UTC } 1 { audioFileName "C3669719-9F0A-4EB5-A791-2C00486665ED-30305-000039A3FDA7DCD2" user "2A8761E4-C13A-470E-A759-91432D61B6AF-25982-0000352D853511AF" audioLanguage "Spanish" date 2012-09-22 01:17:04 UTC } ]

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  • Patterns and conventions to document changes while developing

    - by Talysson
    Let's say I'm developing a second version of an API, and there's some changes in method names and so on from the previous version. What's a good way to document these changes ? I mean, is it better to document while changing (but, maybe, there will be more changes before the release, so I think it could be more work than necessary) or write down some topic and document after all the changes are done ?

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  • Is there a name for a mini class that is not a struct?

    - by user1555300
    I have a couple of mini-classes that are not nested classes. They need to be passed around between different larger classes to use. In a way, they act like Tuples, storing fields in them. For example, [Serializable] public class TransformObject { public GameObject GameObj; public tk2dCameraAnchor Anchor; public ManagerTransform MTransform; } I have a few of them for my game I have been developing. They have to be classes, not struct because the Unity3d editor will not show in the inspector if so. I was just wondering if there is a official name for these kind of mini classes.

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  • Create inherited class from base class

    - by Raj
    public class Car { private string make; private string model; public Car(string make, string model) { this.make = make; this.model = model; } public virtual void Display() { Console.WriteLine("Make: {0}", make); Console.WriteLine("Model: {0}", model); } public string Make { get{return make;} set{make = value;} } public string Model { get{return model;} set{model = value;} } } public class SuperCar:Car { private Car car; private int horsePower; public SuperCar(Car car) { this.car = car; } public int HorsePower { get{return horsePower;} set{horsepower = value;} } public override void Display() { base.Display(); Console.WriteLine("I am a super car"); } When I do something like Car myCar = new Car("Porsche", "911"); SuperCar mySupcar = new SuperCar(myCar); mySupcar.Display(); I only get "I am a supercar" but not the properties of my base class. Should I explicitly assign the properties of my base class in the SuperCar constructor? In fact I'm trying Decorator pattern where I want a class to add behaviour to a base class.

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  • Python: Class factory using user input as class names

    - by Sano98
    Hi everyone, I want to add class atttributes to a superclass dynamically. Furthermore, I want to create classes that inherit from this superclass dynamically, and the name of those subclasses should depend on user input. There is a superclass "Unit", to which I can add attributes at runtime. This already works. def add_attr (cls, name, value): setattr(cls, name, value) class Unit(object): pass class Archer(Unit): pass myArcher = Archer() add_attr(Unit, 'strength', 5) print "Strenght ofmyarcher: " + str(myArcher.strength) Archer.strength = 2 print "Strenght ofmyarcher: " + str(myArcher.strength) This leads to the desired output: Strenght ofmyarcher: 5 Strenght ofmyarcher: 2 But now I don't want to predefine the subclass Archer, but I'd rather let the user decide how to call this subclass. I've tried something like this: class Meta(type, subclassname): def __new__(cls, subclassname, bases, dct): return type.__new__(cls, subclassname, Unit, dct) factory = Meta() factory.__new__("Soldier") but no luck. I guess I haven't really understood what new does here. What I want as a result here is class Soldier(Unit): pass being created by the factory. And if I call the factory with the argument "Knight", I'd like a class Knight, subclass of Unit, to be created. Any ideas? Many thanks in advance! Bye -Sano

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  • A dynamic array of class "landmark", inside another single class "landmarks"

    - by pinnacler
    I'm working on a robot localization simulator and I created a class called "landmark". The end result is going to be a robot that is always centered and always faces the top of the screen. As it turns, the birds eye view map will rotate around the robot. To accomplish this, I'm assuming I can rotate one class and have all elements inside rotate as well. So, the landmark class has properties x,y, label, and radius. This is suppose to simulate a tree location in a forest. To test everything, I need "forest data," and I wrote a script to generate 100 trees in a 100m x 100m area. The script automatically generates values within an acceptable range for x,y, radius. The generated data is stored in an object called tempForest and is 100x3. Ideally, I want to create a class called "landmarks" (plural) that has 100 landmark instances inside. How would I instantiate 100 instances of landmark in one instance of landmarks using that randomly generated data? Ideally, I'd just type treeBeacons = landmarks(); and it would randomly populate 100 (user definable, set in config file) instances with x, y, radius data. I'm not sure how to deal with a dynamic array of class "Landmark", inside another single class "landmarks." Any ideas?

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  • Why does a sub-class class of a class have to be static in order to initialize the sub-class in the

    - by Alex
    So, the question is more or less as I wrote. I understand that it's probably not clear at all so I'll give an example. I have class Tree and in it there is the class Node, and the empty constructor of Tree is written: public class RBTree { private RBNode head; public RBTree(RBNode head,RBTree leftT,RBTree rightT){ this.head=head; this.head.leftT.head.father = head; this.head.rightT.head.father = head; } public RBTree(RBNode head){ this(head,new RBTree(),new RBTree()); } public RBTree(){ this(new RBNode(),null,null); } public class RBNode{ private int value; private boolean isBlack; private RBNode father; private RBTree leftT; private RBTree rightT; } } Eclipse gives me the error: "No enclosing instance of type RBTree is available due to some intermediate constructor invocation" for the "new RBTree()" in the empty constructor. However, if I change the RBNode to be a static class, there is no problem. So why is it working when the class is static. BTW, I found an easy solution for the cunstructor: public RBTree(){ this.head = new RBNode(); } So, I have no idea what is the problem in the first piece of code.

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  • C# class can not disguise to be another class because GetType method cannot be override

    - by zinking
    there is a statement in the CLR via C# saying in C#, one class cannot disguise to be another, because GetType is virutal and thus it cannot be override but I think in C# we can still hide the parent implementation of GetType. I must missed something if I hide the base GetType implementation then I can disguise my class to be another class, is that correct? The key here is not whether GetType is virutal or not, the question is can we disguise one class to be another in C# Following is the NO.4 answer from the possible duplicate, so My question is more on this. is this kind of disguise possible, if so, how can we say that we can prevent class type disguise in C# ? regardless of the GetType is virtual or not While its true that you cannot override the object.GetType() method, you can use "new" to overload it completely, thereby spoofing another known type. This is interesting, however, I haven't figured out how to create an instance of the "Type" object from scratch, so the example below pretends to be another type. public class NotAString { private string m_RealString = string.Empty; public new Type GetType() { return m_RealString.GetType(); } } After creating an instance of this, (new NotAString()).GetType(), will indeed return the type for a string. share|edit|flag answered Mar 15 at 18:39 Dr Snooze 213 By almost anything that looks at GetType has an instance of object, or at the very least some base type that they control or can reason about. If you already have an instance of the most derived type then there is no need to call GetType on it. The point is as long as someone uses GetType on an object they can be sure it's the system's implementation, not any other custom definition. – Servy Mar 15 at 18:54 add comment

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  • Java: Comparing a class with another within that class using a my own .equals

    - by user1670252
    I am making a method .equals replacing the equals method used. It accepts a object. I want it to check if that object equals the class that runs the .equals class. I know I want to compare all the private methods I have to that object. Is there a way to do this without making another private class to get the private variables from the object? How do I do this to compare equality not identity? I am stuck on this. Do i have to use == to compare? Also looking online i see others use recursion. If this is the way i have to do it can you show and explain it to me? so an example i have public boolean equals(Object o) { this is in a class we will call bobtheBuilder (first thing to pop in my head) I want to check if the object o is equal to the class he has private object array and a private int. I assume I want to check if the array and int of this class equal the array and int of the object.

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  • static member specialization of templated child class and templated base class

    - by b3nj1
    I'm trying to have a templated class (here C) that inherits from another templated class (here A) and perform static member specialization (of int var here), but I cant get the right syntax to do so (if it's possible #include <iostream> template<typename derived> class A { public: static int var; }; //This one works fine class B :public A<B> { public: B() { std::cout << var << std::endl; } }; template<> int A<B>::var = 9; //This one doesn't works template<typename type> class C :public A<C<type> > { public: C() { std::cout << var << std::endl; } }; //template<> template<typename type> int A<C<type> >::a = 10; int main() { B b; C<int> c; return 0; } I put an example that works with a non templated class (here B) and i can get the static member specialization of var, but for C that just doesn't work. Here is what gcc tells me : test.cpp: In constructor ‘C<type>::C()’: test.cpp:29:26: error: ‘var’ was not declared in this scope test.cpp: At global scope: test.cpp:34:18: error: template definition of non-template ‘int A<C<type> >::a’ I'm using gcc version 4.6.3, thanks for any help

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