Object Oriented Programming

Object Oriented Programming OOP is programming paradigm based on concept of mapping real world objects to programming objects based on four principles:

1. Abstraction
2. Encapsulation
3. Inheritance
4. Polymorphism

Abstraction

Abstraction principle means that every object should hide unnecessary details and expose only required, minimal interface to interact with.

public abstract class Monster
{
    public abstract void GetDamage(int value);
}

Encapsulation

Encapsulation principle relies on hiding internal state of concrete object by utilizing, for example access modifiers.

Most commonly used access modifiers

• public - accessible by everyone
• private - accessible only by containing class
• protected - accessible by containing and derived classes

public abstract class Monster
{
    private readonly int _maxHealth;

    private int _health;

    public abstract void GetDamage(int value);

    public int Health
    {
        get
        {
            //...
        }
        protected set
        {
            //...
        }
      }
}

Inheritance

Inheritance principle means ability to extend functionality of previously defined objects.

public class Dragon : Monster
{
    public override GetDamage(int value)
    {
        //...
    }
}

public class Hydra : Monster
{
    public override GetDamage(int value)
    {
        //...
    }
}

Polymorphism

Polymorphism principle means ability to refer to object by sub-objects.

var monsters = new List<Monster>
{
    new Hydra("Hydra"),
    new Dragon("Lord")
};

foreach (var monster in monsters)
{
    monster.GetDamage(42);

    //...
}