ssukhpinder

public abstract class AChatroom
{
    public abstract void Register(User user);
    public abstract void Post(string fromUser, string toUser, string msg);
}

ssukhpinder

class Program
{
    static void Main(string[] args)
    {
        ITransactions adapter = new TransAdapter();
        foreach (var item in adapter.GetTransactions())
        {
            Console.WriteLine(item);
        }
    }

ssukhpinder

public class TransAdapter : OrgYTransactions, ITransactions
{
    public List<string> GetTransactions()
    {
        return GetTransactionsList();
    }
}

ssukhpinder

public class OrgYTransactions
{
    public List<string> GetTransactionsList()
    {
        List<string> transactions = new List<string>();
        transactions.Add("Debit 1");
        transactions.Add("Debit 2");
        transactions.Add("Debit 3");
        return transactions;
    }

ssukhpinder

static void Main(string[] args)
{
    var sedan = new ModelSedan();
    var suv = new ModelSuv();

    var factory = new CarFactory();
    var builders = new List<CarBuilder> { suv, sedan };

    foreach (var b in builders)
    {

ssukhpinder

public class ModelSedan : CarBuilder
{
    public override void SetIsSUV()
    {
        _car.IsSUV = false;
    }

    public override void SetName()
    {
        _car.Name = "Maruti Sedan";

ssukhpinder

public class ModelSuv : CarBuilder
{
    public override void SetIsSUV()
    {
        _car.IsSUV = true;
    }

    public override void SetName()
    {
        _car.Name = "Maruti SUV";

ssukhpinder

public class CarFactory
{
    public Car Build(CarBuilder builder)
    {
        builder.SetName();
        builder.SetSpeed();
        builder.SetIsSUV();
        return builder.GetCar();
    }
}

ssukhpinder

public abstract class CarBuilder
{
    protected readonly Car _car = new Car();
    public abstract void SetName();
    public abstract void SetSpeed();
    public abstract void SetIsSUV();
    public virtual Car GetCar() => _car;
}

ssukhpinder

static void Main(string[] args)
{
    var sukhpinder = new Sukhpinder();

    var firstFan = new Follower();
    var secondFan = new Follower();

    sukhpinder.AddFollower(firstFan);
    sukhpinder.AddFollower(secondFan);