abstract

问题 Is there a standard way to make a "pure virtual function" in Swift, ie. one that must be overridden by every subclass, and which, if it is not, causes a compile time error? 回答1: You have two options: 1. Use a Protocol Define the superclass as a Protocol instead of a Class Pro : Compile time check for if each "subclass" (not an actual subclass) implements the required method(s) Con : The "superclass" (protocol) cannot implement methods or properties 2. Assert in the super version of the method

问题 Let's say I have my classic: public abstract class Mammal { private int numLegs; private String voice; private Coat coat; public abstract void eat(); public abstract void speak(); public abstract void sleep(); private abstract void ingestFood(Food f); //The abstract method ingestFood in type Mammal can only set a visibility modifier, one of public or protected } With these concrete implementations: public class Dog extends Mammal { private int numLegs = 4; private String voice = "Woof!";

问题 The C# spec, section 10.1.1.1, states: An abstract class is permitted (but not required) to contain abstract members. This allows me to create classes like this: public abstract class A { public void Main() { // it's full of logic! } } Or even better: public abstract class A { public virtual void Main() { } } public abstract class B : A { public override sealed void Main() { // it's full of logic! } } This is really a concrete class; it's only abstract in so far as one can't instantiate it.

问题 F# does not support the definition of protected methods. Here it is explained why F# replaces virtual methods with abstract methods defined in abstract classes (see here). I was wondering if there is a way to prevent access to abstract methods from outside the derived classes at all. 回答1: Like Patryk Ćwiek, I also don't think it's possible, but here's one alternative: From Design Patterns we know that we should favour Composition over Inheritance . In my experience, everything you can do with

问题 I would like to force SubClasses to @Override method from SuperClass . Method in SuperClass can't be abstract , cause I wanna provide some basic implementation. Here is example of my code: public abstract class GenericModel<T extends GenericModel> { long id, counter; public String methodToBeOverridenInSubClass(String name) { // some basic implementation // rest details will be provided by subclass return name; } } public class SubClass extends GenericModel<SubClass> { @Override public String

问题 I have a parent class in Java called Flight . I have children classes: JetFlight , NormalFlight , etc. which inherit from Flight . I want all the children classes to implement compareTo from the Comparable interface. I want them to inherit from Flight because I want to use polymorphism (for example, initiate a Flight array and fill it with objects of JetFlight , NormalFlight , etc.). This is my code for the parent class: public abstract class Flight { public abstract int compareTo(Object o);

问题 I have a parent class in Java called Flight . I have children classes: JetFlight , NormalFlight , etc. which inherit from Flight . I want all the children classes to implement compareTo from the Comparable interface. I want them to inherit from Flight because I want to use polymorphism (for example, initiate a Flight array and fill it with objects of JetFlight , NormalFlight , etc.). This is my code for the parent class: public abstract class Flight { public abstract int compareTo(Object o);

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