Lecture 26 - Nov 14, 2023

Summary

In this lecture, we continue our discussion on complexity analysis, and how we get evaluate the big-O of recursive functions.

Last lecture

Complexity analysis.

Today

Inheritance.

Inheritance

Inheritance is a pillar of object-oriented programming.

Inheriting/acquiring all properties and behaviours of a parent class.

In Person.h:

class Person {
  private:
    string name;
    int age;

  public:
    Person() { name = ""; age = 0; }
    Person(string n, int a) { name = n; age = a; }
    void setName(string n) { name = n; }
    void print() {
      cout << "Name: " << name << endl;
      cout << "Age: " << age << endl;
    }
};

I want to create a class Student. The data for this class should be: name, age, and ID. The functions should be: setName(), print(), and setNameID().

I can reuse some of the code.

Option 1: From scratch.

Option 2: Copy and paste code from Person class and add setNameID(). The issues are:

1. Understand all details of Person.
2. If you change Person, no changes will be reflected to Student.

Option 3: Inherit from Person. The benefits are:

1. Re-use code.
2. Need to understand what Person does.

Person is a base class.

Student is a derived class.

In Student.h:

class Student : public Person {
  private:
    int ID;

  // age and name are innaccessible

  // we don't inherit constructors of Person

  public:
    Student() : Person() { ID = 0; }

    // setName is inherited
    void setNameID(string n, int d) {
      Person::setName(n);
      ID = d;
    }

    // method overriding: replace/redefine the inherited print() from Person
    // we define our own version for Student
    void print() {
      cout << "ID: " << ID << endl;

      // I can't access age and name
      Person::print();
    }
};

In main.cpp:

#include "Person.h"
#include "Student.h"

using namespace std;

int main() {
  Person p("Joe", 23);

  // name and age are inaccessible
  Student s;

  // 1. we construct Person object
  // 2. On top of it, we construct Student object

  // setName is inherited from Person, so we can call it on Student
  s.setName("Ryan");

  s.setNameID("Marina", 125);
}