polymorphism

问题 For example BaseClass MyBase() { public int Add(BaseClass next) { if (this is InheritedA && next is InheritedA) return 1; else if (this is InheritedA && next is InheritedB) return 2; else if (this is InheritedB && next is InheritedA) return 3; else if (this is InheritedB && next is InheritedB) return 4; } } where InheritedA , and InheritedB are its inherited classes. In fact, there are more Inherited classes, and the Add returns different results based on the order and types of its operand. I

问题 Within a class, a field that has the same name as a field in the superclass hides the superclass's field. public class Test { public static void main(String[] args) { Father father = new Son(); System.out.println(father.i); //why 1? System.out.println(father.getI()); //2 System.out.println(father.j); //why 10? System.out.println(father.getJ()); //why 10? System.out.println(); Son son = new Son(); System.out.println(son.i); //2 System.out.println(son.getI()); //2 System.out.println(son.j); /

问题 I'm creating a rails 3 application that will be decentralized and I need to use UUID as primary key for my tables, what would be the best gem, plugin for the Job. I also would like to know if it is possible to make in ActiveRecord polymorphic relationships without using the polymorphicable_type column for it, given the case that I'm using UUID. I have created a demo http://github.com/boriscy/uuidrails3 that uses UUID as keys, you should check the module UUIDHelper inside lib/ and also all the

问题 I am trying to implement (C#) an interface method in a class, returning a derived type instead of the base type as defined in the interface: interface IFactory { BaseCar GetCar(); } class MyFactory : IFactory { MyCar GetCar() { } } Where, of course: class MyCar : BaseCar { } However, the following error happens: 'MyFactory' does not implement interface member 'IFactory.GetCar()'. 'MyFactory.BaseCar()' cannot implement IFactory.GetCar()' because it does not have the matching return type of

问题 guys, I have a case that needs the child class needs to call its parent virtual function at first before call its override virtual function. BaseClass::Draw() { } ChildClass::Draw() { BaseClass::Draw(); // BaseClass Draw must be called first. } GrandChildClass::Draw() { ChildClass::Draw(); // ChildClass Draw must be called first. } I want to hide this behavior from clients. Is there pattern on this? Thanks. 回答1: For simple cases you can use a second, private member function for the

问题 I am trying to use pointers to create links between objects. Using Fortran and here is the code piece: module base_pars_module type,abstract,public :: base_pars end type end module module test_parameters_module use base_pars_module type, extends(base_pars) :: test_pars contains procedure :: whoami end type contains function whoami(this) result(iostat) class( test_pars) :: this write(*,*) 'i am a derived type child of base_pars' end type end module module base_mask_module use base_pars module

问题 The following code tries to copy an object and keep the original type. Unfortunately it does not work (every copied object will become a Super instead of being of the same class as its original). Please note that copySuper(const Super& givenSuper) should not know anything about the subclasses of Super . Is it possible to do such a copy? Or do I have to change the definition of copySuper ? #include <string> #include <iostream> class Super { public: Super() {}; virtual ~Super() {}; virtual std:

问题 In java, can we pass superclass Object to subclass reference ? I know that it is a weird question/practically not viable, but I want to understand the logic behind this Why is it not allowed in java. class Employee { public void met1(){ System.out.println("met1"); } } class SalesPerson extends Employee { @Override public void met1(){ System.out.println("new met1"); } public void met2(){ System.out.println("met2"); } } public class ReferenceTest { public static void main(String[] args) {

问题 Given the following scenario, I want map the type hierarchy to the database schema using Fluent NHibernate. I am using NHibernate 2.0 Type Hierarchy public abstract class Item { public virtual int ItemId { get; set; } public virtual string ItemType { get; set; } public virtual string FieldA { get; set; } } public abstract class SubItem : Item { public virtual string FieldB { get; set; } } public class ConcreteItemX : SubItem { public virtual string FieldC { get; set; } } public class

问题 This question already has answers here : Closed 8 years ago . Possible Duplicate: How can I simulate OO-style polymorphism in C? I'm trying to better understand the idea of polymorphism with examples from languages I know; is there polymorphism in C? 回答1: This is Nekuromento's second example, factored in the way I consider idiomatic for object-oriented C: animal.h #ifndef ANIMAL_H_ #define ANIMAL_H_ struct animal { // make vtable_ a pointer so they can be shared between instances // use _ to