polymorphism

问题 Here's a test practice question i came across, would appreciate your help in making me understand the concepts Let Hawk be a subclass of Bird. Suppose some class has two overloaded methods void foo(Hawk h) and void foo(Bird b). Which version would get executed in the call foo(x) after the declaration Bird x = new Hawk(); Here's the code i have so far, could someone explain to me why foo(bird b) gets executed? public class MPractice { public static void main(String args[]) { Bird x = new Hawk(

问题 I have a code similar to: Module C_sys use class_A implicit none Private Type, public :: C_sys_type private logical :: Ao_set = .false. type(A) :: Ao Contains Private Procedure, public :: get_Ao Procedure, public :: set_Ao End Type C_sys_type interface C_sys_type Procedure C_sys_type_constructor end interface C_sys_type Contains type(C_sys_type) elemental function C_sys_type_constructor(Ao) result(C_sys) type(A), intent(in), optional :: Ao C_sys % Ao = Ao C_sys % Ao_set = .true. end function

问题 I'm writing a C# game engine for my game, and I've hit a problem. I need to do a XNA.Rectangle drawRectangle for each different type of block. Blocks are stored in a list of blocks, so the property, to be accessible by draw without casting a lot, must be overriden. I've tried lots of ways of doing it, but none work. Here's the current one I'm doing: Block.cs protected static Rectangle m_drawRectangle = new Rectangle(0, 0, 32, 32); public Rectangle drawRectangle { get { return m_drawRectangle;

问题 I am experimenting with Core's List.fold_left . # List.fold_left;; - : 'a Core.Std.List.t -> init:'b -> f:('b -> 'a -> 'b) -> 'b = <fun> It works fine when I specify the labels: # List.fold_left [1;2;3] ~init:0 ~f:(+);; - : int = 6 But I get a different result when I do not specify the labels: # List.fold_left [1;2;3] 0 (+);; - : init:(int -> (int -> int -> int) -> '_a) -> f:((int -> (int -> int -> int) -> '_a) -> int -> int -> (int -> int -> int) -> '_a) -> '_a = <fun> And other partial

问题 I've got the following problem with Jackson and type hierarchy. I'm serializing a class SubA which extends Base into a String , and trying afterwards to derserialize it back. Of course at compile time, the system does not know whether it will be Base or SubA so I'm expecting a Base and will do some other operations afterwards, if it is a SubA . My Base class looks like: @JsonTypeInfo( use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type") @JsonSubTypes({ @Type

问题 Say: Apple is derived from a base Fruit Class, then there is a class ApplePicker derived from a base FruitPicker class. The ApplePicker class has vector<Apple> appleList , the Fruit picker class has a pointer to a vector<Fruit> i.e. vector<fruit>* fruitList . I need to be able to set the vector to this pointer, so abstract methods can be run in the fruit picker class(as they only are concerned with the fruit members). But I am having trouble setting this, when I tried to do this: this-

问题 I have this simple method: public void CacheDelegate(Object obj, MemberInfo memberInfo) { switch (memberInfo.MemberType) { case MemberTypes.Field: var fieldInfo = (FieldInfo) memberInfo; CacheDelegate(obj, fieldInfo); break; case MemberTypes.Property: var propertyInfo = (PropertyInfo) memberInfo; CacheDelegate(obj, propertyInfo); break; case MemberTypes.Method: var methodInfo = (MethodInfo) memberInfo; CacheDelegate(obj, methodInfo); break; default: throw new Exception("Cannot create a

问题 I want to have the following setup: abstract class Parent { public static String ACONSTANT; // I'd use abstract here if it was allowed // Other stuff follows } class Child extends Parent { public static String ACONSTANT = "some value"; // etc } Is this possible in java? How? I'd rather not use instance variables/methods if I can avoid it. Thanks! EDIT: The constant is the name of a database table. Each child object is a mini ORM. 回答1: you can't do it exactly as you want. Perhaps an acceptable

问题 In Strategy Design Pattern , what we do is Create a common interface. Implement a set of classes using that interface with overridden method(s). Let the run time to choose the actual class for an object which has the same type with that common interface and call the overridden method(s) which will resolve correctly according to the class. My question is, Isn't it the basic example of polymorphism and method overriding we learn? other than the possibility of using an abstract class too,

问题 I asked a question earlier but it turns out my problem was not properly modeled by my example. So here is my actual problem: I have class A , and class B inheriting from A , I have two functions foo(A&) and foo(B&) , I have a list of A* pointers, containing instances of A and B . How do I get to call foo(A&) for instances of A and foo(B&) for instances of B ? Constraints: I can modify A and B implementation, but not foo 's implementation. See below an example: #include <iostream> #include