Which of the assignment statements in someMethod are valid? All of them. x, this.x and super.x all point to protected int x in class A which is visible to the subclass B. this.getX() and super.getX() both call public int getX() in class A which is visible to the subclass B. answer, x and the return … Read more
Consider following: public interface Animal { bool isVertebrate(); bool isDomesticable(); } and an abstract class that implements this interface: abstract class Cat implements Animal { public bool isVertebrate() {return true;} public void dealWithCat(){ if (isDomesticable()){ … } } But implementation for isDomesticable is delegated to subclass: public class Tiger extends Cat { public bool isDomesticable(){ … Read more
There must be something wrong with the quiz, the code as written in the question is declaring that MyInt is a subclass of int (or equivalently: that int is the superclass of MyInt), no the other way around. 1 solved Superclass inherits from a subclass. Coursera. Are they crazy? [closed]
For many reasons – code maintainability, extensibility, concision, reliability, minimising the amount of code that needs to be recompiled/redistributed to pick up changes in some library code it uses – you should almost always use virtual functions rather that writing your own switching mechanisms. If you need to ask about it on stackoverflow, I’d go … Read more
having attribute of a base class that is not needed in derived class is a hint for bad inheritance in your case i assume you are going to have another derived class that needs those data members, otherwise it wouldnt make sense then why not do something like this: class Base { public: void f1(void); … Read more
The object that you’re extending,Event, does not have a constructor that takes no arguments. So you need to call super and specify arguments like you do in your other constructor. solved Implicit super constructor Event() is undefined [duplicate]
You create an instance of B that is lets say “Bigger”, but the variable ‘a’ is converted into class A that is “Smaller” and contains the method print A. You did something similar to: A : IClass B : IClass The interface exposes some method that is in both A and B, and you to … Read more
If your method has the same name that the parent’s, parameters and return type, you’re overriding it. Also you can add @Override annotation on the top of your method. Always check parent’s method is not final nor private. For instance public class Parent{ public void method(String param){ //Do stuff } private void notExtendable(String param){ } … Read more
JLS 15.20.2 states: If a cast of the RelationalExpression to the ReferenceType would be rejected as a compile-time error (§15.16), then the instanceof relational expression likewise produces a compile-time error. In such a situation, the result of the instanceof expression could never be true. In this case (Intf) obj is not a compile time error … Read more
So, blah defines an instance field called label but does not initialise it public abstract class Blah { protected JLabel label; } BlahChildOne initialises the label from Blah public class BlahChildOne extends Blah { public BlahChildOne() { label = new JLabel(); } } BlahChildTwo does not initialises the label from Blah, so it is still … Read more
void setvalores(int vi, int fu, int ve) { velocidad = &ve; vida = &vi; fuerza = &fu; }; The pointers to vi, fu, and ve get invalidated when the function returns. You’re not seeing addresses being printed, but simply garbage. Your entire design doesn’t and shouldn’t need to use pointers though. 8 solved Pointer will … Read more
I’m goign to take a shot at it because I recently tried to understand those and this is a good way to see if I did 🙂 because If you can’t explain something you haven’t really understood it 🙂 Casting is fairly simple. It means to pretty much convert a value or object of a … Read more
why should we use inheritance between A (super) & B (sub) instead of creating them separately and instantiate A from B? [closed] solved why should we use inheritance between A (super) & B (sub) instead of creating them separately and instantiate A from B? [closed]
Here’s a version of your first example, that actually uses polymorphism: #include <iostream> #include <string> class shape { public: void setValues(int height_, int width_) { height = height_; width = width_; } virtual int area() = 0; // This is needed for polymorphism to work virtual std::string name() = 0; protected: int height; int width; … Read more
class B { int m() { return new A().m(); } } or class B { private A a = new A(); int m() { return a.m(); } } or class B { private A a; public B(A a) { this.a = a; } int m() { return a.m(); } } solved Inheritance vs. Delegation [duplicate]