Practical Example for Abstract Classes

using System;

namespace AbstractClasses
{
    public abstract class Messager
    {
        protected string _recipient;
        protected string _message;
        public Messager(string recipient, string message)
        {
            _recipient = recipient;
            _message = message;
        }
        public void ProcessMessage()
        {
            LogMessageLength();
            // the code from here
            var isValid = false;
            if (ValidateRecipient())
            {
                isValid = true;
                SendMessage();
            }
            // to here will be implemented by the concrete classes
            if (isValid)
                NotifyTheServiceOwner("The message was correctly sent");
            else
                NotifyTheServiceOwner("The message was NOT sent");
        }
        protected abstract void SendMessage();
        protected abstract bool ValidateRecipient();
        private void LogMessageLength()
        {
            // log the message
            Console.WriteLine("Sending a message of size: {0}", _message.Length);
        }
        private void NotifyTheServiceOwner(string note)
        {
            // notify the service owner via email
        }
    }
    public class SmsMessager : Messager
    {
        public SmsMessager(string _recipient, string _message) 
            : base(_recipient, _message) 
        { }
        protected override bool ValidateRecipient()
        {
            // validate the phone number
            return true;
        }
        protected override void SendMessage()
        {
            // use some SMS service to send the message
        }
    }
    public class EmailMessage : Messager
    {
        public EmailMessage(string _recipient, string _message) 
            : base(_recipient, _message) 
        { }
        protected override bool ValidateRecipient()
        {
            // validate the email address 
            return true;
        }
        protected override void SendMessage()
        {
            // use the .Net classe to send an email
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var messagers = new Messager[] 
            { 
                new EmailMessage("adrian@domain.com","Hello"),
                new SmsMessager("+4074312122", "Hi"),
                new EmailMessage("rahul@domain2.com", "Hello rahul")
            };
            foreach (var messager in messagers)
            {
                messager.ProcessMessage();
            }
        }
    }
}