polymorphism

问题 I would like to have "yet another" callback registration stuff. Different event types extending a common base event type will trigger associated callback functions. here is the initial draft or idea #include <functional> #include <iostream> #include <unordered_map> class BaseEvent { public: virtual ~BaseEvent() {} }; class DerivedEvent_1 : public BaseEvent {}; class DerivedEvent_2 : public BaseEvent {}; // a container holding callback functions std::unordered_map<size_t/*event*/, std:

问题 I am studying up on my Java Programming and Object Oriented Programming. I keep getting hung up on what the benefit of Dynamic Polymorphism is? Take a look at my sample program below. Why would I use example 1 over example 2? class SuperHero { private String power = ("Generic Power"); public void useSuperPower() { System.out.println(power); } } class Spiderman extends SuperHero { private String power = ("Web sling!"); public void useSuperPower() { System.out.println(power); } } class

问题 As far as In understand he getS method from child class BB overrides the same method from the parent class AA . Yet although both classes have initialized the field s which is returned by getS it's printed as null . Why is this happening? This is the code: public class AA { public String getS() { return s; } private String s = "hello1"; public AA() { System.out.println(service() + getS()); } public static String service() { return "A service "; } } public class BB extends AA { private String

问题 As far as In understand he getS method from child class BB overrides the same method from the parent class AA . Yet although both classes have initialized the field s which is returned by getS it's printed as null . Why is this happening? This is the code: public class AA { public String getS() { return s; } private String s = "hello1"; public AA() { System.out.println(service() + getS()); } public static String service() { return "A service "; } } public class BB extends AA { private String

问题 As far as In understand he getS method from child class BB overrides the same method from the parent class AA . Yet although both classes have initialized the field s which is returned by getS it's printed as null . Why is this happening? This is the code: public class AA { public String getS() { return s; } private String s = "hello1"; public AA() { System.out.println(service() + getS()); } public static String service() { return "A service "; } } public class BB extends AA { private String

问题 As far as In understand he getS method from child class BB overrides the same method from the parent class AA . Yet although both classes have initialized the field s which is returned by getS it's printed as null . Why is this happening? This is the code: public class AA { public String getS() { return s; } private String s = "hello1"; public AA() { System.out.println(service() + getS()); } public static String service() { return "A service "; } } public class BB extends AA { private String

问题 Answer: In short use virtual functions! So don't actually use this as good design, but for learning purposes take a read! I want to start off by saying I am using c++ and Qt I have a vector of Shape pointers (Base class) Edit: doSomething() is not a member of the Base class but instead a derived class member. Which is why I am using dynamic_cast to get Shape* to the Derived* so that I can access it. I am really doing this just out of curiosity at this point though and for other peoples

问题 Answer: In short use virtual functions! So don't actually use this as good design, but for learning purposes take a read! I want to start off by saying I am using c++ and Qt I have a vector of Shape pointers (Base class) Edit: doSomething() is not a member of the Base class but instead a derived class member. Which is why I am using dynamic_cast to get Shape* to the Derived* so that I can access it. I am really doing this just out of curiosity at this point though and for other peoples

问题 I am not too familiar with polymorphism, and was wondering if I have it used in my code? If this doesn't contain a polymorphic reference, could you lead me in a direction of where I would need to go? The files that the program is using are not included, as I am mainly curious about whether or not any polymorphic references are used. java file 1 - this file runs the program import java.util.Scanner; public class ADTDemo { ADTDictionary dictionary; public static void menu() { System.out.println

问题 here's my problem. I have a template abstract class RandomVariable with pure virtual function operator()() template<T> class RandomVariable<T> { public: virtual T operator()() = 0; /* other stuff */ protected: T value; } I also have a template abstract class Process with pure virtual function operator()() template<T> class Process<T> { public: typedef std::pair<double, T> state; typedef std::list<state> result_type; virtual result_type operator()() = 0; /* other stuff */ protected: result