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  • what would be the output?

    - by Abhishek Jain
    Please explain me below situation What would be the output? interface A{} class B implements A{} class C extends B{} Class D extends C{} class E extends D{ public static void main(String args[]){ C c = new C(); B b = c; A a = (E)c; A a = (B)c; C c = (C)(B)c; } }

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  • JavaScript inheritance extend function

    - by Zach
    I'm having some trouble understanding the IF clause at the end of this function from Pro JavaScript Design Patterns: function extend(subClass, superClass) { var F = function() {}; F.prototype = superClass.prototype; subClass.prototype = new F(); subClass.prototype.constructor = subClass; subClass.superclass = superClass.prototype; if(superClass.prototype.constructor == Object.prototype.constructor) { superClass.prototype.constructor = superClass; } } The book explains that these lines ensure that the superclass's constructor attribute is correctly set, even if the superclass is the Object class itself. Yet, if I omit those three lines and do the following: function SubClass() {}; extend(SubClass, Object); alert(Object.prototype.constructor == Object); The alert says 'true', which means the superclass's constructor is set correctly even without those last three lines. Under what conditions, then, does this IF statement do something useful? Thanks.

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  • dynamic inheritance without touching classes

    - by Jasper
    I feel like the answer to this question is really simple, but I really am having trouble finding it. So here goes: Suppose you have the following classes: class Base; class Child : public Base; class Displayer { public: Displayer(Base* element); Displayer(Child* element); } Additionally, I have a Base* object which might point to either an instance of the class Base or an instance of the class Child. Now I want to create a Displayer based on the element pointed to by object, however, I want to pick the right version of the constructor. As I currently have it, this would accomplish just that (I am being a bit fuzzy with my C++ here, but I think this the clearest way) object->createDisplayer(); virtual void Base::createDisplayer() { new Displayer(this); } virtual void Child::createDisplayer() { new Displayer(this); } This works, however, there is a problem with this: Base and Child are part of the application system, while Displayer is part of the GUI system. I want to build the GUI system independently of the Application system, so that it is easy to replace the GUI. This means that Base and Child should not know about Displayer. However, I do not know how I can achieve this without letting the Application classes know about the GUI. Am I missing something very obvious or am I trying something that is not possible?

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  • C++ abstract class template + type-specific subclass = trouble with linker

    - by user333279
    Hi there, The project in question is about different endpoints communicating with each other. An endpoint sends events (beyond the scope of the current problem) and can process incoming events. Each event is represented in a generic object as follows: #pragma interface ... // some includes template<typename T> class Event { public: Event(int senderId, Type type, T payload); // Type is an enum Event(int senderId, Type type, int priority, T payload); virtual ~Event(); virtual int getSenderId(); virtual int getPriority(); virtual T getPayload(); void setPriority(const int priority); protected: const int senderId; const Type type; const T payload; int priority; }; It has its implementing class with #pragma implementation tag. An endpoint is defined as follows: #pragma interface #include "Event.h" template<typename T> class AbstractEndPoint { public: AbstractEndPoint(int id); virtual ~AbstractEndPoint(); virtual int getId(); virtual void processEvent(Event<T> event) = 0; protected: const int id; }; It has its implementing class too, but only the constructor, destructor and getId() are defined. The idea is to create concrete endpoints for each different payload type. Therefore I have different payload objects and specific event classes for each type, e.g. Event<TelegramFormatA>, Event<TelegramFormatB> and ConcreteEndPoint for TelegramFormatA, ConcreteEndPoint for TelegramFormatB respectively. The latter classes are defined as class ConcreteEndPoint : AbstractEndPoint<TelegramFormatA> { ... } I'm using g++ 4.4.3 and ld 2.19. Everything compiles nicely, but the linker complaints about undefined references to type-specific event classes, like Event<TelegramFormatA>::Event(....) . I tried explicit instantiation using template class AbstractEndPoint<TelegramFormatA>; but couldn't get past the aforementioned linker errors. Any ideas would be appreciated.

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  • Inheritance and Implicit Type Casting

    - by Josué Molina
    Suppose I have the following three classes: class Animal {}; class Human : public Animal {}; class Dog : public Animal { public: void setOwner(Animal* owner) { this->owner = owner; } private: Animal* owner; }; Why is the following allowed, and what exactly is happening? Dog d; Human h; d.setOwner(&h); // ? At first, I tried to cast it like this d.setOwner(&(Animal)h), but the compiler gave me a warning, and I hit a run-time error. Edit: the warning the compiler gave me was "taking address of temporary". Why is this so?

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  • operator overloading and inheritance

    - by user168715
    I was given the following code: class FibHeapNode { //... // These all have trivial implementation virtual void operator =(FibHeapNode& RHS); virtual int operator ==(FibHeapNode& RHS); virtual int operator <(FibHeapNode& RHS); }; class Event : public FibHeapNode { // These have nontrivial implementation virtual void operator=(FibHeapNode& RHS); virtual int operator==(FibHeapNode& RHS); virtual int operator<(FibHeapNode& RHS); }; class FibHeap { //... int DecreaseKey(FibHeapNode *theNode, FibHeapNode& NewKey) { FibHeapNode *theParent; // Some code if (theParent != NULL && *theNode < *theParent) { //... } //... return 1; } }; Much of FibHeap's implementation is similar: FibHeapNode pointers are dereferenced and then compared. Why does this code work? (or is it buggy?) I would think that the virtuals here would have no effect: since *theNode and *theParent aren't pointer or reference types, no dynamic dispatch occurs and FibHeapNode::operator< gets called no matter what's written in Event.

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  • Perfom python unit tests via a web interface

    - by 47
    Is it possible to perform unittest tests via a web interface...and if so how? EDIT: For now I want the results...for the tests I want them to be automated...possibly every time I make a change to the code. Sorry I forgot to make this more clear

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  • multiple inheritance

    - by hitech
    when we say "a member declated as protected is accessible to any class imediately derived from it" what does this mean. in the follwing example get_number function can be accessible by the result class , as per the statement it sould only be accessile to test class. class student { protected: int roll_number; public: void get_number(int){ cout<< "hello"; } void put_number(void) {cout<< "hello"; } }; class test : public student { protected : float sub1; float sub2; public: void get_marks(float, float) {cout<< "hello"; roll_number = 10; } void put_marks(void) {cout<< "hello"; cout << "roll_number = " << roll_number ; } }; class result :public test { float total; public: void display(){cout<< "hello"; roll_number = 10; } }; int main() { result student; student.get_marks(2.2, 2.2); student.put_marks(); return 0; } i changed the code as per the first statement the protected variable roll_number not be accessible upto the result class ?

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  • image with external interface

    - by Leo
    I need to send a picture to flash with external interface (as3)... can not be an url because don't have connection... I'm trying open the image file and send to flash like text but without success any idea?

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  • Not sure I am using inheritance/polymorphism issue?

    - by planker1010
    So for this assignment I have to create a car class(parent) and a certifiedpreowned (child) and I need to have the parent class have a method to check if it is still under warranty. *checkWarrantyStatus(). that method calls the boolean isCoveredUnderWarranty() to veryify if the car still has warranty. My issue is in the certifiedpreowned class I have to call the isCoveredUnderWarranty() as well to see if it is covered under the extended warranty and then have it be called via the checkWarrantyStatus() in the car method. I hope this makes sense. So to sum it up I need to in the child class have it check the isCoveredUnderWarranty with extended warranty info. Then it has to move to the parent class so it can be called via checkWarrantyStatus. Here is my code, I have 1 error. public class Car { public int year; public String make; public String model; public int currentMiles; public int warrantyMiles; public int warrantyYears; int currentYear =java.util.Calendar.getInstance().get(java.util.Calendar.YEAR); /** construct car object with specific parameters*/ public Car (int y, String m, String mod, int mi){ this.year = y; this.make = m; this.model = mod; this.currentMiles = mi; } public int getWarrantyMiles() { return warrantyMiles; } public void setWarrantyMiles(int warrantyMiles) { this.warrantyMiles = warrantyMiles; } public int getWarrantyYears() { return warrantyYears; } public void setWarrantyYears(int warrantyYears) { this.warrantyYears = warrantyYears; } public boolean isCoveredUnderWarranty(){ if (currentMiles < warrantyMiles){ if (currentYear < (year+ warrantyYears)) return true; } return false; } public void checkWarrantyStatus(){ if (isCoveredUnderWarranty()){ System.out.println("Your car " + year+ " " + make+ " "+ model+ " With "+ currentMiles +" is still covered under warranty"); } else System.out.println("Your car " + year+ " " + make+ " "+ model+ " With "+ currentMiles +" is out of warranty"); } } public class CertifiedPreOwnCar extends Car{ public CertifiedPreOwnCar(int y, String m, String mod, int mi) { super(mi, m, mod, y); } public int extendedWarrantyYears; public int extendedWarrantyMiles; public int getExtendedWarrantyYears() { return extendedWarrantyYears; } public void setExtendedWarrantyYears(int extendedWarrantyYears) { this.extendedWarrantyYears = extendedWarrantyYears; } public int getExtendedWarrantyMiles() { return extendedWarrantyMiles; } public void setExtendedWarrantyMiles(int extendedWarrantyMiles) { this.extendedWarrantyMiles = extendedWarrantyMiles; } public boolean isCoveredUnderWarranty() { if (currentMiles < extendedWarrantyMiles){ if (currentYear < (year+ extendedWarrantyYears)) return true; } return false; } } public class TestCar { public static void main(String[] args) { Car car1 = new Car(2014, "Honda", "Civic", 255); car1.setWarrantyMiles(60000); car1.setWarrantyYears(5); car1.checkWarrantyStatus(); Car car2 = new Car(2000, "Ferrari", "F355", 8500); car2.setWarrantyMiles(20000); car2.setWarrantyYears(7); car2.checkWarrantyStatus(); CertifiedPreOwnCar car3 = new CertifiedPreOwnCar(2000, "Honda", "Accord", 65000); car3.setWarrantyYears(3); car3.setWarrantyMiles(30000); car3.setExtendedWarrantyMiles(100000); car3.setExtendedWarrantyYears(7); car3.checkWarrantyStatus(); } }

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  • inheritance from the django user model results in error when changing password

    - by Jerome
    I inherited form the django user model like so: from django.db import models from django.contrib.auth.models import User, UserManager from django.utils.translation import ugettext_lazy as _ class NewUserModel(User): custom_field_1 = models.CharField(_('custom field 1'), max_length=250, null=True, blank=True) custom_field_2 = models.CharField(_('custom field 2'), max_length=250, null=True, blank=True) objects = UserManager() When i go to the admin and add an entry into this model, it saves fine, but below the "Password" field where it has this text "Use '[algo]$[salt]$[hexdigest]' or use the change password form.", if i click on the "change password form' link, it produces this error Truncated incorrect DOUBLE value: '7/password' What can i do to fix this?

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  • Using inheritance with multiple files in Ruby

    - by Preethi Jain
    I am new to Ruby . I have a question with respect to using Inheritence in Ruby . I have a class called as Doggy inside a file named Doggy.rb class Doggy def bark puts "Vicky is barking" end end I have written another class named Puppy in another file named puppy.rb class Puppy < Doggy end puts Doggy.new.bark I am getting this Error: Puppy.rb:1:in `<main>': uninitialized constant Doggy (NameError) Is it mandatory to have these classes (Doggy and Puppy ) inside a single file only? Edited As per the suggestions , i have tried using require and require_relative as shown , but still i am getting below Error Puppy.rb:1:in `<main>': uninitialized constant Doggy (NameError) class Puppy < Doggy end require_relative 'Doggy.rb' puts Doggy.new.bark

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  • ASP.NET configuration inheritance

    - by NowYouHaveTwoProblems
    I have an ASP.NET application that defines a custom configuration section in web.config. Recently I had a customer who wanted to deploy two instances of the application (for testing in addition to an existing production application). The configuration chosen by the customer was: foo.com - production application foo.com/Testing - test application In this case, the ASP.NET configuration engine decided to apply the settings at foo.com/web.config to foo.com/Testing/web.config. Thankfully this caused a configuration error because the section was redefined at the second level rather than giving the false impression that the two web applications were isolated. What I would like to do is to specify that my configuration section is not inherited and must be re-defined for any web application that requires it but I haven't been able to find a way to do this. My web.config ends up something like this <configuration> <configSections> <section name="MyApp" type="MyApp.ConfigurationSection"/> </configSections> <MyApp setting="value" /> <NestedSettingCollection> <Item key="SomeKey" value="SomeValue" /> <Item key="SomeOtherKey" value="SomeOtherValue" /> </NestedSettingCollection> </MyApp> </configuration>

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  • enable_shared_from_this and inheritance

    - by DeadMG
    I've got a type which inherits from enable_shared_from_this<type>, and another type that inherits from this type. Now I can't use the shared_from_this method because it returns the base type and in a specific derived class method I need the derived type. Is it valid to just construct a shared_ptr from this directly? Edit: In a related question, how can I move from an rvalue of type shared_ptr<base> to a type of shared_ptr<derived>? I used dynamic_cast to verify that it really was the correct type, but now I can't seem to accomplish the actual move.

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