overriding

问题 I\'d like to know: Why can\'t static methods be overridden in Java? Can static methods be overloaded in Java? 回答1: Static methods can not be overridden in the exact sense of the word, but they can hide parent static methods In practice it means that the compiler will decide which method to execute at the compile time, and not at the runtime, as it does with overridden instance methods. For a neat example have a look here. And this is java documentation explaining the difference between

问题 Let\'s assume this scenario in Visual C++ 2010: #include <iostream> #include <conio.h> using namespace std; class Base { public: int b; void Display() { cout<<\"Base: Non-virtual display.\"<<endl; }; virtual void vDisplay() { cout<<\"Base: Virtual display.\"<<endl; }; }; class Derived : public Base { public: int d; void Display() { cout<<\"Derived: Non-virtual display.\"<<endl; }; virtual void vDisplay() { cout<<\"Derived: Virtual display.\"<<endl; }; }; int main() { Base ba; Derived de; ba

问题 After reading through References To Theme Attributes I am trying to reference the value of an attribute in the my custom theme that I have set. I am applying a user-defined style to a CheckedTextView <CheckedTextView android:id=\"@+id/contactInfo\" style=\"@style/ListViewCheckedTextViewRowStyle\" > </CheckedTextView> The user-defined style is defined as : <style name=\"ListViewCheckedTextViewRowStyle\" parent=\"@style/ListViewRowStyle\"> <item name=\"android:checkMark\">?android

问题 There is a possible optimization I could apply to one of my methods, if I can determine that another method in the same class is not overridden. It is only a slight optimization, so reflection is out of the question. Should I just make a protected method that returns whether or not the method in question is overridden, such that a subclass can make it return true? 回答1: I wouldn't do this. It violates encapsulation and changes the contract of what your class is supposed to do without

问题 Why does the compiler give an error message when you reduce the visibility of a method while overriding it in the subclass? 回答1: Because every instance of the subclass still needs to be a valid instance of the base class (see Liskov substitution principle). If the subclass suddenly has lost one property of the base class (namely a public method for example) then it would no longer be a valid substitute for the base class. 回答2: Because if this was allowed, the following situation would be

问题 There have been occasions where I would want to override a method in a class with an extension method. Is there any way to do that in C#? For example: public static class StringExtension { public static int GetHashCode(this string inStr) { return MyHash(inStr); } } A case where I\'ve wanted to do this is to be able to store a hash of a string into a database and have that same value be used by all the classes that use the string class\'s hash (i.e. Dictionary, etc.) Since the built-in .Net

问题 What is the connection between System.out.println() and toString() in Java? e.g: public class A { String x = \"abc\"; public String toString() { return x; } } public class ADemo { public static void main(String[] args) { A obj = new A(); System.out.println(obj); } } If main class runs, it gives an output as \"abc\" . When I remove the code which overrides toString() , it gives an output as \"A@659e0bfd\" . So, can anyone explain what is the working principle of System.out.println() when I

问题 This code: abstract class C { protected abstract void F(D d); } class D : C { protected override void F(D d) { } void G(C c) { c.F(this); } } Generates this error: Cannot access protected member \'C.F(D)\' via a qualifier of type \'C\'; the qualifier must be of type \'D\' (or derived from it) What in the world were they thinking? (Would altering that rule break something?) And is there a way around that aside from making F public? Edit: I now get the reason for why this is (Thanks Greg) but I

问题 I want to implement such code, where B inherit from A and only override A\'s Foo() method, and I hope the code to print B.Foo(), but it still print A.Foo(), it seems that the receiver in Golang can\'t work like this in C++, in which when dynamic binding is enabled, the code can work like what I want. I also post another piece of code, which works, but it\'s too hard to implement, and more like a hack way, I think it\'s not a Golang style. So my problem is: if the parent\'s Bar() method has

问题 Is it possible to override += in Python? 回答1: Yes, override the __iadd__ method. Example: def __iadd__(self, other): self.number += other.number return self 回答2: In addition to what's correctly given in answers above, it is worth explicitly clarifying that when __iadd__ is overriden, the x += y operation does NOT end with the end of __iadd__ method. Instead, it ends with x = x.__iadd__(y) . In other words, Python assigns the return value of your __iadd__ implementation to the object you're