polymorphism

问题 abstract public class car { abstract void drive(); } As in the code snippet above, what exactly is the purpose of an abstract method in Java? From what I can gather, by definition, they aren't allowed to have bodies. 回答1: When you make things implement the same abstract class, you are saying, these things are alike at a high level, but they vary in the particulars of how they do things. An abstract method is how you say, "Here's something that all the things that extend this class have to do,

问题 abstract public class car { abstract void drive(); } As in the code snippet above, what exactly is the purpose of an abstract method in Java? From what I can gather, by definition, they aren't allowed to have bodies. 回答1: When you make things implement the same abstract class, you are saying, these things are alike at a high level, but they vary in the particulars of how they do things. An abstract method is how you say, "Here's something that all the things that extend this class have to do,

问题 With the following example I attempting to learn a few new to me concepts. abstraction polymorphic classes factory programming. boost serialization The nuances of how pointers behave are still something I am working to figure out. Here is a small program that I have written to show you the issue I am struggling to understand. When I unserialize the polymorphic object below I only get an object created from the default constructor. TodoFactory::retrieveATodo is not recreating the object from

问题 With the following example I attempting to learn a few new to me concepts. abstraction polymorphic classes factory programming. boost serialization The nuances of how pointers behave are still something I am working to figure out. Here is a small program that I have written to show you the issue I am struggling to understand. When I unserialize the polymorphic object below I only get an object created from the default constructor. TodoFactory::retrieveATodo is not recreating the object from

问题 I'm banging my head against a polymorphic relationship definition within Laravel 5.7 Here's the data situation: I have a model for Users, a model for Products and a model for Merchandising I basically want to build a WishList for my user, that can contain both Merchandises and Products, and I want to have a polymorphic relationship there because I will have to add new types of things to sell at a later time. In my (simplified) current data schema, I have users -email -id products -id -name

问题 I have a base class that I made a template because I want to vary the type it takes for several functions, but I want to derive from these templated base classes. I want to store a vector of these classes. My idea was to create a non-templated base class above everything in the hierarchy, and use double dispatching to figure out the type. Am I doing this the "right way"? Here's a code snippet of the scenario: class FooBase { public: virtual void Accept( Visitor &v ); }; template<class T>

问题 So I'm using a boost graph of the following type: typedef boost::adjacency_list<boost::listS, boost::vecS, boost:directedS, VertexT, EdgeT> GraphT VertexT and EdgeT are both classes to keep many of the properties I need. These are bundled properties. I'm not sure if some of the ways I want to use bgl are possible so if you are familiar with them help would be much appreciated. VertexT and EdgeT are suppose to be polymorphic base classes. My understanding is bgl is not meant to use for

问题 I am trying to deserialize a JSON Object into a Java Object using Jackson annotation on one Abstact class "Animal": @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type") @JsonSubTypes({@Type(value = Dog.class, name = "chien"), @Type(value = Cat.class, name= "chat")}) and here is a sample JSON string: { "name": "Chihuahua", "type": { "code": "chien", "description": "Chien mechant" } } The problem is that the property "type" in the JSON object is also

问题 I don't know how I didn't notice this, but data constructors and function definitions alike can't use types with kinds other than * and it's variants * -> * etc., due to (->) 's kind signature, even under -XPolyKinds . Here is the code I have tried: {-# LANGUAGE DataKinds #-} {-# LANGUAGE KindSignatures #-} data Nat = S Nat | Z data Foo where Foo :: 'Z -> Foo -- Fails foo :: 'Z -> Int -- Fails foo _ = 1 The error I'm getting is the following: <interactive>:8:12: Expected a type, but ‘Z’ has

问题 I'm writing a game in C++ that has about 30 different roles that are each slightly different. I have a main class User that contains all of the data required by all of the roles. My first implementation involved just having an enumeration of 30 roles and handling appropriately, but now I'm wondering if it would be better to have User as a base class and each role being its own class that inherits from User. My main concern is how efficient are polymorphic method calls when there are 30+