overriding

问题 We always say that method overloading is static polymorphism and overriding is runtime polymorphism. What exactly do we mean by static here? Is the call to a method resolved on compiling the code? So whats the difference between normal method call and calling a final method? Which one is linked at compile time? 回答1: Method overloading means making multiple versions of a function based on the inputs. For example: public Double doSomething(Double x) { ... } public Object doSomething(Object y) {

问题 In C++, will a member function of a base class be overridden by its derived class function of the same name, even if its prototype (parameters' count, type and constness) is different ? I guess this a silly question, since many websites says that the function prototype should be the same for that to happen; but why doesn't the below code compile? It's a very simple case of inheritance, I believe. #include <iostream> using std::cout; using std::endl; class A {}; class B {}; class X { public:

问题 I would like someone to try and explain the difference between these. More specifically, example usage scenario's. I am refactoring some Windows Form code and a Form has some code in the Form_Load() event and also in a protected override void OnLoad() event that calls base.OnLoad(e); Now I traced it and the Override fires first and then immediately fires off the event version. So, which one is typically used and why? 回答1: You should always override OnLoad(). Using the event is only

问题 I'm preparing for the SCJP (recently rebranded as OCPJP by Oracle) and one particular question that I got wrong on a mock exam has confused me, the answer description doesn't explain things clear enough. This is the question : class A { int x = 5; } class B extends A { int x = 6; } public class CovariantTest { public A getObject() { return new A(); } public static void main(String[]args) { CovariantTest c1 = new SubCovariantTest(); System.out.println(c1.getObject().x); } } class

问题 How can I call the eat and drink method of the Animal class with the myAnimal instance in the code? public class Animal { public void eat() { System.out.println("Animal Eats"); } public void drink() { System.out.println("Animal Drinks"); } } public class Cat extends Animal { @Override public void eat() { System.out.println("Cat Eats"); } @Override public void drink() { System.out.println("Cat Drinks"); } public static void main(String[] args) { Cat myCat = new Cat(); myCat.eat(); myCat.drink(

问题 I am trying to write a class library that can catch the windows messages to notify me if a device has been attached or removed. Normally, in a windows forms app I would just override the WndProc method but there is not WndProc method in this case. Is there another way I can get the messages? 回答1: You'll need a window, there's no way around that. Here's a sample implementation. Implement an event handler for the DeviceChangeNotifier.DeviceNotify event to get notifications. Call the

问题 I am trying to write a class library that can catch the windows messages to notify me if a device has been attached or removed. Normally, in a windows forms app I would just override the WndProc method but there is not WndProc method in this case. Is there another way I can get the messages? 回答1: You'll need a window, there's no way around that. Here's a sample implementation. Implement an event handler for the DeviceChangeNotifier.DeviceNotify event to get notifications. Call the

问题 Is there is any reason to make the permissions on an overridden C++ virtual function different from the base class? Is there any danger in doing so? For example: class base { public: virtual int foo(double) = 0; } class child : public base { private: virtual int foo(double); } The C++ faq says that it is a bad idea, but doesn't say why. I have seen this idiom in some code and I believe that the author was attempting to make the class final, based on an assumption that it is not possible to

问题 Is there is any reason to make the permissions on an overridden C++ virtual function different from the base class? Is there any danger in doing so? For example: class base { public: virtual int foo(double) = 0; } class child : public base { private: virtual int foo(double); } The C++ faq says that it is a bad idea, but doesn't say why. I have seen this idiom in some code and I believe that the author was attempting to make the class final, based on an assumption that it is not possible to

问题 This question already has answers here : Is the 'override' keyword just a check for a overridden virtual method? (5 answers) Closed 6 years ago . I am a beginner in C++. I have come across override keyword used in the header file that I am working on. May I know, what is real use of override , perhaps with an example would be easy to understand. 回答1: The override keyword serves two purposes: It shows the reader of the code that "this is a virtual method, that is overriding a virtual method of