inheritance

问题 i have 4 classes Product and MultiBuyProduct (which is a child of product) which are used to work out price, and a shopping cart which you can add to which calls functions from MultiBuyProduct gets their price and prints a receipt to console, and Amount which is a class that takes 2 ints and does some calculations on them eg add subtract and then returns a formatted price. from my main.cpp i call MultiBuyProduct p2("Wine", Amount(10,0), 2, 10); ShoppingCart SC; SC.add(&p2 ,2, true); below

问题 I'm working on a project where I need to extend WebClient for a custom implementation, MyWebClient . I also need to make sure that MyWebClient is the only version that's implemented by any developer on the project and no one uses the base WebClient class. Is it possible to prevent the usage of WebClient , considering it's not code that I have access to? 回答1: Depending on the features of WebClient you need, you could consider implementing MyWebClient as proxy that exposes only the methods you

问题 I was wondering if someone could explain to me how I might be able to implement something similar to this: namespace advanced_cpp_oop { class A { B b; }; class B : public A { }; } int main() { } Where an instance of a base class can contain an instance of a derived class? When the above code is compiled the following error is generated: g++ advanced_cpp_oop.cpp advanced_cpp_oop.cpp:8:5: error: ‘B’ does not name a type The (almost) equivalent Java code which does compile is: public class

问题 I have a model with some inherits and it is using nhibernate to persisti on a Database. The nhibernate mapping with fluent nhibernate is working fine, but I have a scenario where I need to save a child for a existent parent. My model looks like this: public class Item { public long Id { get; set; } public string Name { get; set; } // other properties } public class ItemCommercial : Item { public decimal Value { get; set; } // other properties } In my Database, the respective tables are

问题 I'm trying to build a chess game in C++. I have a base class gamePiece and a derived class rook. My original idea was to create a vector of gamePiece objects and insert all of the different types of gamePieces (rooks, queens, pawns) inside there. As I found out in my last question, I can't do that -- the gamePiece vector only takes base class (i.e. gamePiece) objects. However, smart pointers and other techniques were suggested. I will try that soon. But I'm still curious as to why the

问题 I have: class A : IHelp class B : IHelp Then I want to do such thing like: List<A> alist = new List<A>(); List<IHelp> hList = (List<IHelp>) alist; // Error!!! I am a beginner programmer. I will be very grateful to you for detailed answer. Thanks for help! 回答1: You cannot do a cast like this, because it will violate the constraints of the original list. Suppose this works like you said (it actually gives an error, but assume it works): List<A> aList = new List<A>(); List<IHelp> hList = aList;

问题 Suppose I have the following four classess, out of which two are abstract and two are concrete: Abstract1 , Concrete1 , Abstract2 , Concrete2 . Concrete1 extends Abstract1 and Concrete2 extends Abstract2 . Suppose I have the following four classess, out of which two are abstract and two are concrete: AbstractProp , ConcreteProp , AbstractClass , ConcreteClass . ConcreteProp extends AbstractProp and ConcreteClass extends AbstractClass . The code for AbstractClass would look like the following:

问题 I'm a bit confused about how Java generics handle inheritance / polymorphism. Assume the following hierarchy - Animal (Parent) Dog - Cat (Children) So suppose I have a method doSomething(List<Animal> animals) . By all the rules of inheritance and polymorphism, I would assume that a List<Dog> is a List<Animal> and a List<Cat> is a List<Animal> - and so either one could be passed to this method. Not so. If I want to achieve this behavior, I have to explicitly tell the method to accept a list of

问题 I have an interface that is used by several classes and the interface implementation is the same for all the classes. I would make it a base abstract class, but then it would stop the deriving classes from inhering from another class later on, which I need. So instead of reimplementing the same interface in all the classes, can I somehow implement the interface in one place, like an .h file and include the .h file in the cs file so the class "implements" the interface. By the way, the

问题 All I want to do is similar to: public abstract class BaseClass { public static Type GetType() { return typeof(BaseClass); } } But when I derive it public class DerivedClass : BaseClass { } I want to get Assert.AreEqual(typeof(DerivedClass), DerivedClass.GetType()); How to change the BaseClass to make this assertion true? 回答1: Static methods are not inherited. The compiler substitutes BaseClass for DerivedClass when calling a base class' static methods through one of its derived classes. For