polymorphism

问题 I'm going to use Entity Framework soon for a Booking System ( made from scratch ). I have been doing a few Prototypes, trying to figure out what I want to do before the project is started (I'm still discussing requirements etc. with the client). Consider this case: I have a Booking, and a booking can have associated Ressources, that can be booked, but these ressource can be different, and have different Fields etc. I have never really used EF before, so I don't know how I can achieve this

问题 I'm Java person who just started learning Python. Take this example: class Person(): def __init__(self, name, phone): self.name = name self.phone = phone class Teenager(Person): def __init__(self, name, phone, website): self.name=name self.phone=phone self.website=website I'm sure there's a lot of redundant code (I know in Java, there are a lot of redundancies for the bit of code above). Which parts are redundant with respect to which attributes are already inherited from the parent class?

问题 Say we have: Class Base { virtual void f(){g();}; virtual void g(){//Do some Base related code;} }; Class Derived : public Base { virtual void f(){Base::f();}; virtual void g(){//Do some Derived related code}; }; int main() { Base *pBase = new Derived; pBase->f(); return 0; } Which g() will be called from Base::f() ? Base::g() or Derived::g() ? Thanks... 回答1: The g of the derived class will be called. If you want to call the function in the base, call Base::g(); instead. If you want to call

问题 I read that the new modifer hides the base class method. using System; class A { public void Y() { Console.WriteLine("A.Y"); } } class B : A { public new void Y() { // This method HIDES A.Y. // It is only called through the B type reference. Console.WriteLine("B.Y"); } } class Program { static void Main() { A ref1 = new A(); // Different new A ref2 = new B(); // Polymorpishm B ref3 = new B(); ref1.Y(); ref2.Y(); //Produces A.Y line #xx ref3.Y(); } } Why does ref2.Y(); produce A.Y as output?

问题 I have a particular scenario below. The code below should print 'say()' function of B and C class and print 'B says..' and 'C says...' but it doesn't .Any ideas.. I am learning polymorphism so also have commented few questions related to it on the lines of code below. class A { public: // A() {} virtual void say() { std::cout << "Said IT ! " << std::endl; } virtual ~A(); //why virtual destructor ? }; void methodCall() // does it matters if the inherited class from A is in this method { class

问题 Let's say we have a class foo which has a private instance variable bar . Now let us have another class, baz , which extends foo . Can non-static methods in baz access foo 's variable bar if there is no accessor method defined in foo ? I'm working in Java, by the way. 回答1: No, not according to the java language specification, 3rd edition: 6.6.8 Example: private Fields, Methods, and Constructors A private class member or constructor is accessible only within the body of the top level class (§7

问题 assume that class Dog extends class Animal: why this polymorphic statement is not allowed: List<Animal> myList = new ArrayList<Dog>(); However, it's allowed with plain arrays: Animal[] x=new Dog[3]; 回答1: The reasons for this are based on how Java implements generics. An Arrays Example With arrays you can do this (arrays are covariant as others have explained) Integer[] myInts = {1,2,3,4}; Number[] myNumber = myInts; But, what would happen if you try to do this? Number[0] = 3.14; //attempt of

问题 Let's take this simple Java code: public class Animal { public void eat() { System.out.println("Generic Animal Eating Generically"); } } public class Horse extends Animal { public void eat() { System.out.println("Horse eating hay "); } public void eat(String s) { System.out.println("Horse eating " + s); } } I'm trying to figure out which version of the three eat() methods will run. Now, when I type Animal a = new Animal(); a.eat(); The output is "Generic Animal Eating Generically", which is

问题 I have a base class class ShapeF { public: ShapeF(); virtual ~ShapeF(); inline void SetPosition(const Vector2& inPosition) { mPosition.Set(inPosition); } protected: Vector2 mPosition; } Obviously with some ommitied code, but you get the point. I use this as a template, and with some fun (ommited) enums, a way to determine what kind of shape i'm using class RotatedRectangleF : public ShapeF { public: RotatedRectangleF(); virtual ~RotatedRectangleF(); protected: float mWidth; float mHeight;

问题 I had thought that Generics in C# were implemented such that a new class/method/what-have-you was generated, either at run-time or compile-time, when a new generic type was used, similar to C++ templates (which I've never actually looked into and I very well could be wrong, about which I'd gladly accept correction). But in my coding I came up with an exact counterexample: static class Program { static void Main() { Test testVar = new Test(); GenericTest<Test> genericTest = new GenericTest