abstract-class

问题 Can I add a final procedure to an abstract type? Suppose the final procedure looks like this: subroutine finalize(this) type(bin_tree_t), intent(inout) :: this deallocate(this%head) end subroutine finalize My compiler (ifort 18.0.1) gives "error #8313: The TYPE(derived-type-spec) shall not specify an abstract type". I get this, but the dummy argument of a final subroutine cannot be polymorphic. If this is not possible, is it then likely to have been a conscious choice of the standards

问题 I have a class A that has to extend class B and C which are both provided by 3rd party and I don't have a control of them. Since Java doesn't support multiple inheritance. Using interface wouldn't help in my case since I do want to inherit the base classes' implementation and I don't want to copy their code over to my class, or I'll need to be aware of all their coming changes. What would be the best way to accomplish this need? All suggestion will be much appreciated! 回答1: class A class B2

问题 I have an abstract class element and a child class elasticFrame : class element { public: virtual Matrix getStiffness() = 0; protected: Matrix K; }; class elasticFrame3d:public element { public: elasticFrame3d(double E, double G); virtual Matrix getStiffness(); virtual Matrix getTransform(); private: double E, G; }; what I want is to make a map like this: map<int, element> elementMap; but when I get this error: error C2259: 'element' : cannot instantiate abstract class is it even possible to

问题 I have an abstract class element and a child class elasticFrame : class element { public: virtual Matrix getStiffness() = 0; protected: Matrix K; }; class elasticFrame3d:public element { public: elasticFrame3d(double E, double G); virtual Matrix getStiffness(); virtual Matrix getTransform(); private: double E, G; }; what I want is to make a map like this: map<int, element> elementMap; but when I get this error: error C2259: 'element' : cannot instantiate abstract class is it even possible to

问题 I have two questions really. I'm trying to get a handle on how inheritance works. If I have an abstract class to inherit from, and it has a method that is not labelled abstract does this method still need to be implemented in the subclass? If I have a subclass that is inheriting from another subclass, which is then inheriting from an abstract class, does the lowest subclass need to implement the methods in the abstract class? Or because the methods have been implemented in the middle subclass

问题 As described in this post, I created an abstract base controller class in order to be able to pass data from a controller to master.page. In this case, I want to lookup a user in my db, querying for User.Identity.Name (only if he is logged in). However, I noticed that in this abstract base class the User property is always null . What do I have to do to get this working? Thanks a lot 回答1: As Paco suggested, the viewdata isn't initialized till after you are trying to use it. Try overriding

问题 We are using Jersey/Jackson to unmarshall JSON data to java DTOs. One of my DTO is an abstract class, and i would like to unmarshall the JSON data to one of his extended DTO. For example, assuming i have these DTOs : public abstract class AnimalDTO{} public class DogDTO extends AnimalDTO{} public class CatDTO extends AnimalDTO{} I would like to unmarshall this JSON data: {Zoo: {Animals:[{"type"="DogDTO", "code"="001", "name"="chihuahua"}, {"type"="CatDTO", "code"="002", "name"="felix"}]}} As

问题 I need to have a std::vector of boost::ptr_vector s. To make their management easier, I enclosed the boost::ptr_vector in a class ( Zoo ) and made a std::vector of it ( allZoos ). Look at a minimal code for reproducing this: #include <boost/ptr_container/ptr_vector.hpp> #include <boost/utility.hpp> class Animal { public: virtual char type() = 0; }; class Cat : public Animal { public: char type() { return 1; } }; class Zoo { public: boost::ptr_vector<Animal> animals; }; int main() { std:

问题 the code below is not giving me the answer i want, i don't know where is the problem? FR is the translation of EN (exactly like .properties file) i want to read the translation from the FR.java file if i want to reach the hello variable of fr.java or en.java from the index.jsp page. but code i wrote gives me the value from Lang.java String language = "FR"; the condition is in the .jsp file jdk 1.4 gives me this error :Error(23,23): variable lang might not have been initialized any body can

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