inheritance

问题 So I've been working on a homework on abstraction for my programming class and fell into a problem. The goal for me right now is to be able to use abstraction, then later be able to draw with rectangles and ovals a simple city, like a rectangular building or a oval light on a light post. The error I am receiving when I compile is: MyTestApp.Rectangle is not abstract and does not override abstract method drawEllipse(java.awt.Graphics) in MyTestApp.Shape. This Error shows up on the line "class

问题 Can private methods be overridden in Java? If no, then how does the following code work? class Base{ private void func(){ System.out.println("In Base Class func method !!"); }; } class Derived extends Base{ public void func(){ // Is this a Method Overriding..???? System.out.println("In Derived Class func method"); } } class InheritDemo{ public static void main(String [] args){ Derived d = new Derived(); d.func(); } } 回答1: No, you are not overriding it. You can check by trying to mark it with

问题 I want to do something like this: List<Child> childList = new List<Child>(); ... List<Parent> parentList = childList; However, because parentList is a List of Child's ancestor, rather than a direct ancestor, I am unable to do this. Is there a workaround (other than adding each element individually)? 回答1: Casting directly is not allowed because there's no way to make it typesafe. If you have a list of giraffes, and you cast it to a list of animals, you could then put a tiger into a list of

问题 I want to do something like this: List<Child> childList = new List<Child>(); ... List<Parent> parentList = childList; However, because parentList is a List of Child's ancestor, rather than a direct ancestor, I am unable to do this. Is there a workaround (other than adding each element individually)? 回答1: Casting directly is not allowed because there's no way to make it typesafe. If you have a list of giraffes, and you cast it to a list of animals, you could then put a tiger into a list of

问题 I want to do something like this: List<Child> childList = new List<Child>(); ... List<Parent> parentList = childList; However, because parentList is a List of Child's ancestor, rather than a direct ancestor, I am unable to do this. Is there a workaround (other than adding each element individually)? 回答1: Casting directly is not allowed because there's no way to make it typesafe. If you have a list of giraffes, and you cast it to a list of animals, you could then put a tiger into a list of

问题 If I have something like class Base { static int staticVar; } class DerivedA : public Base {} class DerivedB : public Base {} Will both DerivedA and DerivedB share the same staticVar or will they each get their own? If I wanted them to each have their own, what would you recommend I do? 回答1: They will each share the same instance of staticVar . In order for each derived class to get their own static variable, you'll need to declare another static variable with a different name. You could then

问题 function a () { return "foo"; } a.b = function () { return "bar"; } function c () { }; c.prototype = a; var d = new c(); d.b(); // returns "bar" d(); // throws exception, d is not a function Is there some way for d to be a function, and yet still inherit properties from a ? 回答1: Based on a discussion on meta about a similar question I'm posting this answer here based on @alexander-mills original This can now be done in a standards compliant way First create an object which inherits Function

问题 function a () { return "foo"; } a.b = function () { return "bar"; } function c () { }; c.prototype = a; var d = new c(); d.b(); // returns "bar" d(); // throws exception, d is not a function Is there some way for d to be a function, and yet still inherit properties from a ? 回答1: Based on a discussion on meta about a similar question I'm posting this answer here based on @alexander-mills original This can now be done in a standards compliant way First create an object which inherits Function

问题 Here is what I'd like to do: function a() { // ... } function b() { // Some magic, return a new object. } var c = b(); c instanceof b // -> true c instanceof a // -> true b instanceof a // -> true Is it possible? I can make b be an instance of a easily by hooking a into its prototype chain but then I have to do new b() , which is what I'm trying to avoid. Is what I want possible? Update: I feel that it might be possible with judicious use of b.__proto__ = a.prototype . I'm going to experiment

问题 I have 2 classes one includes methodA and the other include methodB. So in a new class I need to override the methods methodA and methodB. So how do I achieve multiple inheritance in objective C? I am little bit confused with the syntax. 回答1: Objective-C doesn't support multiple inheritance, and you don't need it. Use composition: @interface ClassA : NSObject { } -(void)methodA; @end @interface ClassB : NSObject { } -(void)methodB; @end @interface MyClass : NSObject { ClassA *a; ClassB *b; }