inheritance

问题 So, I have a base class that I want to extend most (but not all) of my domain classes from. The goal is that I can add the six audit information columns I need to any domain class with a simple extends . For both creation and updates, I want to log the date, user, and program (based on request URI). It's using a Grails service (called CasService) to find the currently logged on user. The CasService then uses Spring Security and a database call to get the relevant user information for that

问题 So, I have a base class that I want to extend most (but not all) of my domain classes from. The goal is that I can add the six audit information columns I need to any domain class with a simple extends . For both creation and updates, I want to log the date, user, and program (based on request URI). It's using a Grails service (called CasService) to find the currently logged on user. The CasService then uses Spring Security and a database call to get the relevant user information for that

问题 Have a class Car with a public method public Car myself() { return this; } Have a subclass Ferrari , and a variable foo that contains a Ferrari object. Finally, Ferrari bar = foo.myself(); This will warn you, because the method myself() returns a Car object, rather than the expected Ferrari . Note: I know that the example is stupid because you'd just do bar = foo . It's just an example. Solutions: Override the myself() method in Ferrari . Cast the Car object to a Ferrari object when assigning

问题 I present my question in this simple form: class animal { public: animal() { _name="animal"; } virtual void makenoise(){ cout<<_name<<endl; } string get_name(){ return _name; } protected: string _name; }; class cat : public animal { public: cat() { this->_name="cat"; } }; class dog : public animal { public: dog() { this->_name = "dog"; } }; I want to store all animal types together in a single container such as: vector<animal*> container; barnyard.push_back(new animal()); barnyard.push_back

问题 I've got a super-class (GraphNode) and sub-class (AStarNode). Both can be a member by another class thats why I turned the class which uses it into a generic class (GraphEdge). Inside this class I'd like to call some member-functions of the super-class but the compiler complains that: The method addEdge(GraphEdge<T>) is undefined for the type T How can I fix this or is my approach even ok? Here's some code that better describes the scenario: public class GraphNode { protected Graph graph;

问题 I have a method set in my superclass... public void explain() { for (Item item: Instances) { System.out.println(item.getname + " is in location " + item.place): } } I need to override this same method in the subclass to print out the original output message but the new instance for this method needs to print out different values that have been set in the subclass I'm confused with the overriding bit (as I know little about it) and would like an explanation. 回答1: So just give the method in

问题 I have a class called DBDriver that handles communication with a given table in a database. Its public entry point is a function template called execute_query() , which executes SELECT queries. Upon calling this function, some database logic is performed, and then a provided container (of the template type) is populated with results. This looks something like the following: class DBDriver { ... template <typename CONT_T> void execute_query(const std::string& query, CONT_T& container); ... };

问题 Why can't I create a class in VB.NET that inherits System.IO.Directory ? According to Lutz Roeder, it is not declared as NotInheritable ! I want to create a utility class that adds functionality to the Directory class . For instance, I want to add a Directory.Move function. Please advise and I will send you a six pack. OK nevermind I'm not sending you anything but if you come to the bar tonight I will hook you up and then beat you in pool. 回答1: From the Meta Data of .NET namespace System.IO {

问题 I have the following entity class: [System.ComponentModel.DataAnnotations.Schema.Table("User")] public class User: UserBase, IPersistCustom<Entity> { ... } Depending on the type of hierarchy mapping you use, EF will generate either a descriptor column or split tables. Is there a way to have EF completely ignore the fact that this class inherits from something or implements an interface? I don't mean just ignoring base class properties. 回答1: If you mark your base class(es) as abstract and use

问题 I have the following entity class: [System.ComponentModel.DataAnnotations.Schema.Table("User")] public class User: UserBase, IPersistCustom<Entity> { ... } Depending on the type of hierarchy mapping you use, EF will generate either a descriptor column or split tables. Is there a way to have EF completely ignore the fact that this class inherits from something or implements an interface? I don't mean just ignoring base class properties. 回答1: If you mark your base class(es) as abstract and use