Strategy Design Pattern

Program.cs

using System;

namespace StrategyPattern
{
    //strategy
    public interface IPaymentStrategy
    {
        void Pay(double amount);
    }
    //concrete strategy
    public class Cash : IPaymentStrategy
    {
        public void Pay(double amount)
        {
            Console.WriteLine("{0} paid in cash.", amount);
        }
    }
    //concrete strategy
    public class CreditCard : IPaymentStrategy
    {
        public void Pay(double amount)
        {
            Console.WriteLine("{0} paid via Credit Card", amount);
        }
    }
    //concrete strategy
    public class DebitCard : IPaymentStrategy
    {
        public void Pay(double amount)
        {
            Console.WriteLine("{0} paid via Debit Card", amount);
        }
    }
    //context
    public class Customer
    {
        public IPaymentStrategy Strategy { get; set; }
        public Customer(IPaymentStrategy strategy)
        {
            Strategy = strategy;
        }
        public void Payment(double amount)
        {
            Strategy.Pay(amount);
        }
    }
    class Program
    {
        //entry point
        static void Main(string[] args)
        {
            Customer customer = new Customer(new CreditCard());
            Console.WriteLine("{0} Current Strategy {1} {2}", new string('-',10),
                customer.Strategy.GetType().Name, new string('-', 10));
            customer.Payment(200);

            customer.Strategy = new Cash();
            Console.WriteLine("{0} Current Strategy {1} {2}", new string('-', 10), 
                customer.Strategy.GetType().Name, new string('-', 10));
            customer.Payment(100);

            customer.Strategy = new DebitCard();
            Console.WriteLine("{0} Current Strategy {1} {2}", new string('-', 10), 
                customer.Strategy.GetType().Name, new string('-', 10));
            customer.Payment(500);

            Console.Read();
        }
    }
}