abstract-class

问题 Wait, before you start thinking, I would like to clear that I am NOT going to ask the routine differences between Interface and Abstract. I had gone through the difference between Abstract and Interface in MSDN. It is said : By updating the base class, all inheriting classes are automatically updated with the change. Interfaces, on the other hand, cannot be changed once created. If a new version of an interface is required, you must create a whole new interface. See this : - Can anyone prove

问题 I'm writing some code using a simple clone pattern, I'd like it if I were able to force derived classes to override that clone pattern, but retain the ability to use my base class. (So I don't want to declare the clone method to be pure virtual.) Is there anyway to enforce this restriction at the compiler level? 回答1: Unfortunately there is just no way to make this happen in C++. You can't force a non-abstract method to be overridden in child classes. However, I might note that concrete base

问题 Sorry for the larger amount of the source code. There three abstract classes P, L, PL. The third class PL is derived from classes P and L using the virtual inheritance: template <typename T> //Abstract class class P { public: virtual ~P() = 0; virtual P <T> *clone() const = 0; }; template <typename T> P<T>::~P() {} template <typename T> P<T> * P <T>:: clone() const { return new P <T> ( *this ); } template <typename T> //Abstract class class L { public: virtual ~L() = 0; virtual L <T> *clone()

问题 I would like to create a abstract static method in an abstract class . I am well aware from this question that this is not possible in Java. What is the default workaround / alternative way of thinking of the problem / is there an option for doing this for seemingly valid examples (Like the one below)? Animal class and subclasses: I have a base Animal class with various subclasses. I want to force all subclasses to be able to create an object from an xml string. For this, it makes no sense

问题 I'm looking for ideas on the best way to refactor this scenario (better design, minimal effort). Starting from the following example abstract class (actual has many more fields, methods and abstract methods) : abstract class Car { private int manufactureYear; // ... many more fields that are hard to clone public Car(int manYear) { this.manufactureYear = manYear; } abstract public Color getColor(); abstract public int getNumCylinders(); } There are so many child classes (say 100) that extend

问题 i have to create a fake DMV program that calculates annual fees, for commercial and private vehicles. Those two classes will be abstract and they will polymophism from a class named all vehicles. My instructor wants only one object created the entire program(in main) but since my top 3 tier classes are abstract. I can't create an object with them i.e. vehicles = new vehicles(); so my question is how do i create only one object since they are abstract? If you have any questions feel free to

问题 I want to define a constructor in an abstract class that will create concrete subclasses. abstract class A { type Impl <: A def construct() : Impl = { val res = new Impl() //compile error: class type required but A.this.Impl found // do more initialization with res } } class B extends A {type Impl = B} class C extends A {type Impl = C} //... val b = new B b.construct() // this should create a new instance of B What is wrong here? Is this even possible to implement? EDIT: Clarification: I want

问题 I know it's legal to have a main method in an abstract class, because Eclipse allows me to do the following and run the class as a java application. But does it make sense to do something like this? Is there a real world scenario where one would need to have a main method in an abstract class? public abstract class Automobile { public Boolean powerOn() { // generic implementation for powering on an automobile return true; } public void move() { // generic implementation for move } public void

问题 I think I understand the difference between interface and abstract. Abstract sets default behavior and in cases of pure abstract, behavior needs to be set by derived class. Interface is a take what you need without the overhead from a base class. So what is the advantage of interface over composition? The only advantage I can think is use of protected fields in the base class. What am I missing? 回答1: An interface defines how you will be used. You inherit in order to be reused. This means you

问题 I have an EF4 Model that is built with abstract entities/classes: Notice how State entity has a navigational property called Country . Note: I have lazy-loading disabled, so i must eager-load on demand. Now, if i have the following method: public Location FindSingle(int id) { return _repository.Find().WithId(id).SingleOrDefault(); } This does not return any associations by default. But how can i dynamically eager-load the associations when i explicitly want to? I cannot do this: return