Inheritance Principle

Inheritance is a way of extending class. The new class (child class) builds logic on the top of the parent class (super class).

Here's an example:

using System;

namespace ConsoleApp1
{

class Vehicle
    {
        protected String make;
        protected String model;

public void representation()
        {
            Console.WriteLine(this.make + " " + this.model);
        }

public double getInsuranceCost(int months)
        {
            return 0;
        }

public String getMake()
        {
            return this.make;
        }

public String getModel()
        {
            return this.model;
        }
    }

// Car inherits Vehicle:
    class Car : Vehicle
    {
        // Adds class member:
        private int doorsCount;

// Overwriting method:
        public double getInsuranceCost(int months)
        {
            return months * 25;
        }

// Adding constructor:
        public Car(String makeValue, String modelValue,
        int doorsCountValue)
        {
            this.make = makeValue;
            this.model = modelValue;
            this.doorsCount = doorsCountValue;
        }

// Method extension:
        public void representation()
        {
            base.representation();
            Console.WriteLine( "Doors count: " + doorsCount);
        }

// Adding new method:
        public int getDoorsCount()
        {
            return this.doorsCount;
        }
    }

class Program
    {
        static void Main(string[] args)
        {
            Car car = new Car("Toyota", "Corolla", 4);

// Method that was extended:
            car.representation();

Console.WriteLine("------");
            // Method that was added:
            Console.WriteLine(car.getDoorsCount());
            Console.WriteLine("------");

// Methods that weren't changed:
            Console.WriteLine("Make: " + car.getMake());
            Console.WriteLine("Model: " + car.getModel());
            Console.WriteLine("------");

// Method that was overwritten:
            Console.WriteLine("Insurance cost: " +
                    car.getInsuranceCost(12) + " $");
        }
    }
}

Output:

Basically the child class can add, extend, rewrite or use the inherited logic from the parent.

For this example:

Added logic:
- member - doorsCount (line 36)
- parametrized constructor (line 45)
- getter for doorsCount (line 61)
Extended logic:
- representation method (line 54)
Entirely rewritten logic:
- getInsuranceCost (line 39)
Not modified logic:
- getMake (line 21)
- getModel (line 26)