Question

Discuss the importance of the protected access modifier. Provide examples of when to make parent class data fields private versus protected and how a derived class can access the constructor of its parent class. Consider how the parent/child relationship is enforced with the keyword and the importance of inheritance in application development. Also, discuss how multiple inheritance is commonly used in object-oriented programming languages.

Answer 1

Variables, methods(function) and constructors(class constructors) which are declared protected in the parent can only be accessed by the subclasses (or child classes) in other package or any class .The protected access modifier cannot be given to class and interfaces.

If the fields that are declared private ie. Variables, methods(function) and constructors(class constructors) in base class then they cannot be accessed by any derived or child class .

Example -

#include <bits/stdc++.h>
using namespace std;

// base class Parent
class Parent
{ //private data member
private:
int private_id;
   // protected data members
   protected:
   int proctected_id;
Parent(){
cout<<"Parent constructor"<<endl;
}
  
};

// child class or sub class
class Child : public Parent
{
  
  
   public:
   void setId(int id)
   {
//child class can access the protected_id of the parent class as is is declared protectected
       proctected_id = id;
//the below line which I have commented wont be executed because Child class cannot access the private property of parent class
//if you uncomment the below line and run the program it will give you error that private memebers cannot be accessed
//private_id = id;
      
   }
  
   void displayId()
   {
//it will print the id
       cout << "proctected_id is:" << proctected_id << endl;

//the below line which I have commented wont be executed because Child class cannot access the private property of parent class
//if you uncomment the below line and run the program it will give you error that private memebers cannot be accessed
//cout << "private_id is:" << private_id << endl;
   }
};

// main function
int main() {
   //this will call parent class contructor also
   Child child1;
  
   child1.setId(81);
   child1.displayId();
   return 0;
}

Multiple Inheritance is a feature of object-oriented programming languages where a class can inherit from more than one classes. All the object oriented language supports multiple inheritance except java.

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