inheritance

问题 I know this question has been asked a lot, but the usual answers are far from satisfying in my view. given the following class hierarchy: class SuperClass{} class SubClass extends SuperClass{} why does people use this pattern to instantiate SubClass: SuperClass instance = new SubClass(); instead of this one: SubClass instance = new SubClass(); Now, the usual answer I see is that this is in order to send instance as an argument to a method that requires an instance of SuperClass like here:

问题 I know this question has been asked a lot, but the usual answers are far from satisfying in my view. given the following class hierarchy: class SuperClass{} class SubClass extends SuperClass{} why does people use this pattern to instantiate SubClass: SuperClass instance = new SubClass(); instead of this one: SubClass instance = new SubClass(); Now, the usual answer I see is that this is in order to send instance as an argument to a method that requires an instance of SuperClass like here:

问题 I know this question has been asked a lot, but the usual answers are far from satisfying in my view. given the following class hierarchy: class SuperClass{} class SubClass extends SuperClass{} why does people use this pattern to instantiate SubClass: SuperClass instance = new SubClass(); instead of this one: SubClass instance = new SubClass(); Now, the usual answer I see is that this is in order to send instance as an argument to a method that requires an instance of SuperClass like here:

问题 public class Base { public String Method1() { System.out.println("Inside Base method 1"); return ""; } } class Child extends Base { static Base o = null; public String Method1() { System.out.println("Inside Base method 1"); return ""; } public String Method2() { return "Cant be called with base reference"; } public static void main(String[] args) { // TODO Auto-generated method stub Base base = new Child(); base.Method1(); base.Method2();***(Error : **The method Method2() is undefined for the

问题 public class Base { public String Method1() { System.out.println("Inside Base method 1"); return ""; } } class Child extends Base { static Base o = null; public String Method1() { System.out.println("Inside Base method 1"); return ""; } public String Method2() { return "Cant be called with base reference"; } public static void main(String[] args) { // TODO Auto-generated method stub Base base = new Child(); base.Method1(); base.Method2();***(Error : **The method Method2() is undefined for the

问题 This answer shows how a simple ES6 class: class A { constructor() { this.foo = 42; } bar() { console.log(this.foo); } } is equivalent the following ES5 code: function A() { this.foo = 42; } A.prototype.bar = function() { console.log(this.foo); } Is is similarly possible to translate ES6 class inheritance to ES5 code? What would be the ES5 equivalent to following derived class? class B extends A { constructor() { super(); this.foo2 = 12; } bar() { console.log(this.foo + this.foo2); } baz() {

问题 Can someone please explain how to ensure that the derived function is called from a pointer of type base to a derived object instead of the base function... Also, are the virtual and override keywords best practice to accomplish this? I had previously defined each overload with keyword friend in each class; but the base function was called for the base pointer to derived object. int main() { // contrived example ... base* ptr_derived = new derived(); std::cout << *ptr_derived; delete ptr

问题 I have a pretty simple and straightforward question. What is the standardized way, or the right way, of calling another constructor of a class, along with the base constructor of such class? I understand that the second example does not work. It just seems hackish to be doing it the third way. So what is the way that the people who designed C# expected users to do this? For example: public class Person { private int _id; private string _name; public Person() { _id = 0; } public Person(string

问题 This... class A(object): class B(A): def __init__(self): pass ... throws "NameError: name 'A' is not defined". Is there proper syntax to accomplish this, or must I use workarounds, like this? class A(object): pass class _B(A): pass A.B = _B The prior is strongly preferable. Thank you. 回答1: As per OPs request, posting as an answer. That's an inner class, not a subclass. No, an inner class can't inherit (not extend) its outer class because the outer class is not fully defined while defining the

问题 Let's say that i have a base class Animal. public abstract class Animal; This animal class has the abstract method: public abstract T Copy<T>() where T : Animal When this method is overridden in the Lion class: public class Lion : Animal { string roar = "Roar"; } i wish to return a copy of this lion without its references. So what i think it should be overridden like is this: public abstract T Copy<T>() { return new Lion(){ roar = this.roar; } } but this is not allowed, because Lion cannot be