abstract-class

问题 I understand that in abstract classes methods be both abstract, or not. But why can I not create an abstract method in a "normal", non-abstract class? Thanks in advance for any explanation! 回答1: Abstract method basically says, that there is no implementation of the method and it needs to be implemented in a subclass . However if you had an abstract method in a non-abstract class, you could instantiate the class and get an object, that would have an unimplemented method, which you would be

问题 I recently came across Traits in PHP and I'm trying to understand them. During my research I stumbled upon this Stack Overflow question: Traits vs. Interfaces. The accepted answer mentions the following: An interface defines a set of methods that the implementing class must implement. When a trait is use'd the implementations of the methods come along too--which doesn't happen in an Interface. So far so good but this sounds exactly like the difference between an interface and an abstract

问题 I know that there have been similar questions. The examples given in them are too fragmentary and unclear. I need to edit the entities through a form on the page that sends the POST. The standard method is a method in the controller uses the parameter with @ModelAttribute and validator. If one form serves some subclass of an abstract class, there are no problems with the generation of the necessary fields, but there is a problem in the controller. As I understand it, @ModelAttribute works

问题 I know that there have been similar questions. The examples given in them are too fragmentary and unclear. I need to edit the entities through a form on the page that sends the POST. The standard method is a method in the controller uses the parameter with @ModelAttribute and validator. If one form serves some subclass of an abstract class, there are no problems with the generation of the necessary fields, but there is a problem in the controller. As I understand it, @ModelAttribute works

问题 Can have an abstract class implementing all of its methods -- with no abstract methods in it. Eg.: public abstract class someClass { int a; public someClass (int a) { this.a = a; } public void m1 () { /* do something */ } private void m2 () { /* do something else */ } } What's the advantage, if any, of having such an abstract class compared to having the same class as a concrete one instead? One i can think of is that, when i declare it as abstract, it won't be instantiated. however, i can

问题 I recently reworked one of my own libraries to try out separating interface from implementation. I am having on final issue with a class that is meant to return an instance of another class. In the interface definition, I do something like struct IFoo { virtual const IBar& getBar() = 0; } and then in the concrete Foo getBar looks like const IBar& Foo::getBar() { Bar ret = Bar(); return ret; } The problem is ret gets deleted as soon as getBar is done, causing a big crash when the copy

问题 I recently reworked one of my own libraries to try out separating interface from implementation. I am having on final issue with a class that is meant to return an instance of another class. In the interface definition, I do something like struct IFoo { virtual const IBar& getBar() = 0; } and then in the concrete Foo getBar looks like const IBar& Foo::getBar() { Bar ret = Bar(); return ret; } The problem is ret gets deleted as soon as getBar is done, causing a big crash when the copy

问题 I have some similar entities and I want to create a generic abstract class for CRUD operations for them, but I don't know how can access to entities in generic class. For example: public abstract class HeaderRepository<T> { public HeaderRepository() { } public virtual byte[] Insert(T item) { using (MyEntities context = new MyEntities()) { context.***** <-- What I should write to add an object to entity T } } } I hope I've got it. 回答1: You need to set your DB set. It would be better to have a

问题 How can I create an abstract constructor for an abstract class? For example, if I have this abstract class: export abstract class Foo<T> extends Bar<T> { constructor(someParam: any) { super(); this.someObj = someParam; } } Then it is consumed by this class: export class FooImpl extends Foo<SomeType> { } If I don't override the constructor then the default parameterless constructor will be used on the FooImpl class which will lead to an improper state within the class. How can I define an

问题 I realise that the solution I have here is far from ideal with C++, so I'm asking what a proper C++ programmer would do in this situation. (C++11) I have a DialogBox class, which stores a collection of buttons. At the moment I have a pure abstract inner class DialogBox::Button with the pure virtual function virtual void callback() const . From Java I'm used to using this strategy to create and instantiate an anonymous class deriving from Button in-place which implements the callback function.