Abstract,Interfaces,Virtual usage in C# Demo

OOPinCsharpDemo.cs

using System;

public interface IBasicAbilities
{
    void MotherLanguage ();
}

public abstract class Entity
{
    protected string name;
    protected bool isAlive;
    protected int numberOfLegs;

    public void IsAlive ()
    {
        if (isAlive)
        {
            Console.WriteLine (this.GetType () + " : " + name + " is Alive.");
        }
        else
        {
            Console.WriteLine (this.GetType () + " : " + name + " is not Alive.");
        }
    }

    public void HowManyLegs ()
    {
        Console.WriteLine (this.GetType () + " : " + name + " has : " + numberOfLegs + " legs.");
    }

    public void GetName ()
    {
        Console.WriteLine (this.GetType () + " is named : " + name);
    }

    public virtual void isHungry ()
    {
        Console.WriteLine (name + " needs to be fed !");
    }

    public abstract void isHappy ();

}

public class Human : Entity, IBasicAbilities
{

    string language;

    public Human (string userName, bool userIsAlive, int userNumberOfLegs, string userLanguage)
    {
        name = userName;
        isAlive = userIsAlive;
        numberOfLegs = userNumberOfLegs;
        language = userLanguage;
    }

    public override void isHappy ()
    {
        Console.WriteLine (this.GetType () + " named  " + name + " is happy !");
    }

    public void MotherLanguage ()
    {
        Console.WriteLine (name + " speaks " + language);
    }

}

public class Furniture : Entity
{
    public Furniture (string userName, bool userIsAlive, int userNumberOfLegs)
    {
        name = userName;
        isAlive = userIsAlive;
        numberOfLegs = userNumberOfLegs;
    }

    public override void isHappy ()
    {
        Console.WriteLine ("A " + this.GetType ().Name.ToLower () + " like a " + name.ToLower () + " can't be happy...or sad.");
    }

    public override void isHungry ()
    {
        Console.WriteLine ("A " + this.GetType ().Name.ToLower () + " doesn't get hungry.");
    }

}

public class Plant : Entity
{

    public Plant (string userName, bool userIsAlive, int userNumberOfLegs)
    {
        name = userName;
        isAlive = userIsAlive;
        numberOfLegs = userNumberOfLegs;
    }

    public override void isHappy ()
    {
        Console.WriteLine ("No cause you forgot to water the " + name);
    }

}

public class Test
{
    public static void Main ()
    {
        Human subject1 = new Human ("Brodude", true, 2, "english");
        subject1.GetName ();
        subject1.IsAlive ();
        subject1.HowManyLegs ();
        subject1.isHappy ();
        subject1.isHungry ();
        subject1.MotherLanguage ();

        Furniture subject2 = new Furniture ("Chair", false, 4);
        subject2.GetName ();
        subject2.IsAlive ();
        subject2.HowManyLegs ();
        subject2.isHappy ();
        subject2.isHungry ();

        Plant subject3 = new Plant ("Venus flytrap", true, 0);
        subject3.GetName ();
        subject3.IsAlive ();
        subject3.HowManyLegs ();
        subject3.isHappy ();
        subject3.isHungry ();

        //IBasicAbilities subject4 = new Human("Test", false, 2, "german");
        //subject4.MotherLanguage();
        //Human subject4 = new Human("Test", false, 2, "german");
        //subject4.GetName();
        //subject4.IsAlive();
        //subject4.HowManyLegs();
        //subject4.isHappy();
        //subject4.isHungry();
        //subject4.MotherLanguage();

    }
}

/*--- Output ---
Human is named : Brodude
Human : Brodude is Alive.
Human : Brodude has : 2 legs.
Human named  Brodude is happy !
Brodude needs to be fed !
Brodude speaks english
Furniture is named : Chair
Furniture : Chair is not Alive.
Furniture : Chair has : 4 legs.
A furniture like a chair can't be happy...or sad.
A furniture doesn't get hungry.
Plant is named : Venus flytrap
Plant : Venus flytrap is Alive.
Plant : Venus flytrap has : 0 legs.
No cause you forgot to water the Venus flytrap
Venus flytrap needs to be fed !
*/