Abstraction in C#

1. Abstract Class = Incomplete Design

Can't create object from it. Used as base only.

public abstract class Car
{
    public abstract void Start(); // No code here. Child MUST write it
    public void Honk() { Console.WriteLine("Beep"); } // Normal method OK
}
// Car c = new Car(); // Error: Cannot create abstract class

2. Child Must Implement

public class SportsCar : Car
{
    public override void Start() { Console.WriteLine("VROOM!"); } // Required
}

SportsCar s = new SportsCar();
s.Start(); // VROOM!
s.Honk(); // Beep - inherited

1. Why Abstraction? Force a Contract

Every Car MUST know how to Start. But each starts differently.

public abstract class Car
{
    public string Owner;
    public abstract void Start(); // Every child MUST implement
    public abstract void Stop(); // Every child MUST implement
}

2. Abstract vs Interface

3. Abstract Properties

public abstract class Car
{
    public abstract int MaxSpeed { get; } // Child must define
}

public class SportsCar : Car
{
    public override int MaxSpeed => 300; // Required
}

4. Real-World: Template Method

public abstract class Car
{
    public void Drive() // Template - same for all cars
    {
        Start(); // Step 1: child defines
        Console.WriteLine("Driving...");
        Stop(); // Step 2: child defines
    }
    public abstract void Start();
    public abstract void Stop();
}