abstract-class

问题 I had an interview where interviewer asked me first what is the difference between abstract class with all the methods abstract and an interface. I replied that if it is required to inherit something in the future you will not be able to do it if you have already extended a class. Then, he stated that it was a situation where one would never have to extend any other class and you have to implement a contract. In this circumstance, which would be better, an abstract class or an interface? I

问题 I know the fundamentals of OOP concepts[Inheritance, Abstraction, Encapsulation, Polymorphism] We use Inheritance in case of Parent-Child relationship[Child can have all functionalities which Parent have and can add more functionality to itself too] And we use Abstract class (In java) for a partial set of default implementations of methods in a class, which also can be implemented by simple Inheritance. Look below example which makes my point clear. Inheritance: Parent class public class

问题 This question already has an answer here : Why do gcc and clang allow me to construct an abstract class? (1 answer) Closed 3 years ago . I would like to understand why the compiler allows the following code to compile #include <iostream> struct A { A() { std::cout << "A::A\n"; } virtual void f() const = 0; }; void g(const A& a) { a.f(); } int main() { g({}); } It even outputs A::A when run. If I replace g({}) with g(A()) it obviously doesn't compile. It complains that A is abstract and cannot

问题 HttpServlet is an abstract class with all implemented methods. Why it is abstract? The most common answer I got is, to restrict the instantiation of HttpServlet . But there are other ways of doing it, like a private constructor will restrict the instantiation. I can understand that they are following Template Method design pattern. If some methods are abstract, user will end up implementing all of them, even if he does not need them for his business logic. But if HttpServlet was not abstract,

问题 I just found an article on a framework in Java that apparently allows it to support Mixins and something called Composite Oriented Programming (which for all I know might even be the same thing...) I've also heard of/worked with AOP, and I'm not sure how it differs from this either... 回答1: At a language-agnostic level, a mixin just adds functionality to a class, and is more for programmer convenience and to avoid code duplication. An abstract (base) class forms an is-a relationship and allows

问题 I am trying to design one Abstract class and method in Android and call those methods by extending the class from my parent Activity class but i don't how to call my abstract method. MyCode : MainActivity.java public class MainActivity extends MyActivity { @Override public void onTest() { Log.d("MyLog", "onTest"); } } MyActivity.java public abstract class MyActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);

问题 I will only have a single Abstract Class in this particular module and so I'm trying to avoid importing the "ABC" package. See below for my attempt and the issue I'm running into. I only want to use basic self.attribute = {etc...} assignment in the __init__ method of the subclass but I want to ensure it is done via the AbstractClass. I've seen some questions here but the answers all reference "ABC" package which I would agree is the best solution but not for simply one class in an entire

问题 import java.awt.*; import java.awt.event.*; public class QuadraticSolver extends Frame implements ActionListener, WindowListener { private TextField tfX2; private TextField tfX; private TextField tfNum; private TextField tfVal1; private TextField tfVal2; private TextField tfRoots; private Label lblX2; private Label lblX; private Label lblNum; private Label lblVal1; private Label lblVal2; private Label lblRoots; private Button btnCheckRoots; private Button btnCalc; private Button btnClear;

问题 will the clone method of Asub be called by doing this? Or is Asub deep cloned properly? If not, is there a way to propery deep clone Asub through this kind of method? abstract class Top extends TopMost { protected Object clone() { Object obj = super.clone(); // deep copy and try catch } } abstract class A extends Top { protected Object clone() { Object obj = super.clone(); // deep copy and try catch } } class Asub extends A { protected Object clone() { Object obj = super.clone(); // deep copy

问题 I have this simple piece of code. abstract class X { X() { read(); } private void read() { Object obj = new Object(); readValue(obj); } protected abstract void readValue(Object obj); } class Y extends X { Object obj = null; Y() { super(); } @Override protected void readValue(Object obj) { this.obj = obj; } void printer() { System.out.println("Object = " + obj); } } class Runner { public static void main(String[] args) { Y y = new Y(); y.printer(); } } When I run the above code, the object