Question

47. What is overriding? Describe using java code showing an example of overriding.

48. Does Java allow us to refine behavior in subclasses? If so, show Java code that demonstrates
this property.

49. Does Java allow us to replace behavior in subclasses? If so, show Java code that demonstrates
this property.

50. Can dynamic binding be used in C++? If so, show how this is accomplished.

51. Is there a cost to providing the dynamic binding capability? If so, describe the cost with an example.

Answer 1

47- Object-oriented programming language,provides a feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its super-classes or parent classes called as OVERRIDING. When a method in a subclass has the same name, same parameters or signature and same return type(or sub-type) as a method in its super-class, then the method in the subclass is said to override the method in the super-class.

// A Simple Java program to demonstrate

// method overriding in java

  

// Base Class

class Parent

{

    void show() { System.out.println("Parent's show()"); }

}

  

// Inherited class

class Child extends Parent

{

    // This method overrides show() of Parent

    @Override

    void show() { System.out.println("Child's show()"); }

}

  

// Driver class

class Main

{

    public static void main(String[] args)

    {

        // If a Parent type reference refers

        // to a Parent object, then Parent's

        // show is called

        Parent obj1 = new Parent();

        obj1.show();

  

        // If a Parent type reference refers

        // to a Child object Child's show()

        // is called. This is called RUN TIME

        // POLYMORPHISM.

        Parent obj2 = new Child();

        obj2.show();

    }

}

OUTPUT

Parent's show()
Child's show()

48-Normally, subclassing refines a class by adding variables and methods (you cannot remove or hide variables or methods by subclassing). For example

    class Animal {
        float weight;
        ...
        void eat() {
            ...
        }
        ...
    }

    class Mammal extends Animal {
        // inherits weight
        int heartRate;
        ...

        // inherits eat()
        void breathe() {
            ...
        }
    }

class Cat extends Mammal {
        // inherits weight and heartRate
        boolean longHair;
        ...

        // inherits eat() and breathe()
        void purr() {
            ...
        }
    }

49-In Java, all non-static methods are "virtual", meaning that they are based on the runtime type of the underlying object rather than the type of the reference that points to that object. Therefore, it doesn't matter which type you use in the declaration of the object, the behaviour will be the same.

50​​​​- In C++ we have the facility to specify that the compiler should match function calls with the correct definition at the run time; this is called dynamic binding or late binding or run-time binding. Dynamic binding is achieved by virtual functions. Base class pointer points to derived class object. And a function is declared virtual in base class, then the matching function is identified at run-time using virtual table entry.

using namespace std;
class A
{
public:
virtual void display()
{
cout<<"Base";
}
};

class B:public A
{
public:
void display()
{
cout<<"Derived";
}
};
int main()
{
B b;
A *a=&b;
a->display();
return 0;
}

51-The cost is negligible. It doesn't matter how many classes you have, or how many levels of inheritance, the cost of a polymorphic call is a simple addition.