Inheritance in C#

1. The Base Design = Parent Class

This is the general Car we built last time. All cars have this.

public class Car
{
    public string Owner;
    protected int Speed; // protected: Children can access
    
    public void Start() { Console.WriteLine($"{Owner}'s car started"); }
}

2. The Specialized Design = Child Class

: means "inherits from". SportsCar gets Owner, Speed, and Start() for free.

public class SportsCar : Car // SportsCar IS-A Car
{
    public bool HasTurbo; // Only SportsCar has this
    
    public void ActivateTurbo()
    {
        Speed += 50; // OK: Can access protected Speed from parent
        Console.WriteLine($"Turbo! Speed: {Speed}");
    }
}

3. Using It

SportsCar kunalCar = new SportsCar();
kunalCar.Owner = "Kunal"; // Inherited from Car
kunalCar.HasTurbo = true; // Specific to SportsCar
kunalCar.Start(); // Inherited from Car
kunalCar.ActivateTurbo(); // Specific to SportsCar

1. Why Inheritance? Avoid Copy-Paste

Without inheritance, a SportsCar and Sedan would duplicate code:

public class Sedan { public string Owner; public void Start(){...} }
public class SportsCar { public string Owner; public void Start(){...} public bool HasTurbo; }

If you fix a bug in Start(), you must fix it twice. Inheritance solves this.

2. The base Keyword: Calling Parent

Use base to call parent constructor or methods.

public class Car
{
    protected int Speed;
    public Car(string owner) { Owner = owner; }
    public virtual void Start() { Console.WriteLine("Car started"); }
}

public class SportsCar : Car
{
    public SportsCar(string owner) : base(owner) // Call parent constructor
    {
        Console.WriteLine("SportsCar ready");
    }
    
    public override void Start() // Replace parent method
    {
        base.Start(); // Call parent's Start first
        Console.WriteLine("VROOM! Sports mode on");
    }
}

3. protected: The Family Secret

Remember access modifiers? protected exists for inheritance.

public class Car
{
    private int engineNumber; // Only Car
    protected int Speed; // Car + Children like SportsCar
    public string Owner; // Everyone
}

public class SportsCar : Car
{
    void Tune() {
        Speed = 200; // OK: protected
        // engineNumber = 1; // Error: private
    }
}

Car c = new Car();
// c.Speed = 100; // Error: protected not accessible outside

4. virtual and override: Changing Behavior

virtual = "Child classes are allowed to change this". override = "I am changing it".

public class Car
{
    public virtual void Honk() { Console.WriteLine("Beep"); }
}

public class SportsCar : Car
{
    public override void Honk() { Console.WriteLine("LOUD BEEP!"); }
}

Car myCar = new SportsCar();
myCar.Honk(); // Output: LOUD BEEP! Calls child version

Without virtual/override, it would print "Beep". This is polymorphism.

5. sealed: Stop Inheritance

sealed class cannot be inherited. sealed method cannot be overridden further.

public sealed class FinalCar : Car { } // OK
// public class Another : FinalCar {} // Error: FinalCar is sealed

6. C# Rule: One Parent Only

A class can only inherit from 1 class. public class FlyingCar : Car, Airplane {} is illegal. C# avoids the "diamond problem". For multiple behaviors, use interfaces later.