abstract-class

问题 Are there some practical programming situations for someone to declare a class abstract when all the methods in it are concrete? 回答1: Well you could be using a template method pattern where there are multiple override points that all have default implementations but where the combined default implementations by themselves are not legal - any functional implementation must subclass. (And yes, I dislike the template method pattern ;)) 回答2: An abstract class is a class that is declared abstract

问题 I want to loop through an array of pointers to an abstract class to find an "empty" slot, that is to check whether an element points to an object of a derived class or not. My approach is to create the array and set each element to nullptr. Then, I can check if the element is nullptr. This works, but is there a better way? Edit: Can I check for the first "empty" element in the array of pointers to an abstract class (in which derived classes will periodically be constructed and pointed to by

问题 I've got a abstract baseclass, this is used for deriving some classes. Some properties of these classes are shared among all classes, and these should be unmodifiable. To make a variable shared among all 10 classes I'll make it static. class ABC{ public: static int *anArray; int index; static int tot_index; virtual void print()=0; ABC(){index=tot_index++;}; virtual ~ABC(){}; }; This works fine, tot_index will contain the number of classes instantiated, and the index is the unique indentifier

问题 The issue I am having is with a dropped item i pick up adding ammo to a gun. Built a Gun class with all the methods and variables. Built a Rifle class derived from the Gun class The Rifle works perfect No Issues I now am adding a "PickUp" system where x amount of enemies drop a pickup. This is the script on the item to pick up public class AddARAmmo : MonoBehaviour { private Rifle rifle; private void Awake() { rifle = FindObjectOfType<Rifle>(); } private void OnTriggerEnter(Collider other) {

问题 This question already has answers here : Is there a way to override class variables in Java? (17 answers) Closed 3 years ago . In Java, I have had several projects recently where I used a design pattern like this: public abstract class A { public abstract int getProperty(); } public class B extends A { private static final int PROPERTY = 5; @Override public int getProperty() { return PROPERTY; } } Then I can call the abstract method getProperty() on any member of class A . However, this seems

问题 Can the abstract modifier appear before a class, a method or a variable? 回答1: Abstract can be put in a class declaration, as in public abstract class Test{ //class implementation } ...and in a method declaration, as in public abstract void test(); On the argument: http://java.sun.com/docs/books/tutorial/java/IandI/abstract.html 回答2: The Modifiers Matrix answers your question: class: yes method: yes variable: no 回答3: The abstract modifier is placed before classes or methods. For a class, it

问题 Sometimes I am working with relatively complex (and sometimes confusing - with the way they are laid out by whoever wrote it originally) abstract classes. When inheriting from it, I sometimes encounter cannot instantiate abstract class and most of the time it is because I forgot to declare & implement a pure virtual function. Can I get more information from the compiler about which function it found I did not implement instead of hunting for it? 回答1: Are you using Visual Studio? If so, then

问题 For the following generic c# class, I'd like to convert T to K: public abstract class ValueType<T,K> : IValueType<T> where K : ValueType<T,K>,new() { public abstract T Value { get; set; } public static implicit operator ValueType<T,K>(T val) { K k = new K(); k.Value = val; return k; } } If I were to implement a direct operator implicit operator K(T val) it would result in a compile-time error (CS0556). I thought I could try chaining implicit operators: public static implicit operator K

问题 First of all, pretty new in java, sorry if it is a simple question. I have implemented an abstract class, and two classes that extends it. public abstract class Lado{ //body } and the two other classes with this form for example public class Arista extends Lado { //body } so, no problem there, now i have an interface defined like this. public interface Grafo { //body public List<Lado> lados(); //more body } has you see the interface returns a List of class Lado, but in my implementation I

问题 I have an abstract class with a protected variable abstract class Beverage { protected string description; } I can't access it from a subclass. Intellisense doesn't show it accessible. Why is that so? class Espresso:Beverage { //this.description ?? } 回答1: Short answer: description is a special type of variable called a "field". You may wish to read up on fields on MSDN. Long answer: You must access the protected field in a constructor, method, property, etc. of the subclass. class Subclass {