C#

'AbstractChild.Child.GetInt()' hides inherited member 
'AbstractChild.AbstractChild.GetInt()'. 
To make the current member override that implementation,
 add the override keyword. Otherwise add the new keyword.

public abstract class Base {
  public int GetInt() {
    return 1;
  }
}

public abstract class AbstractChild : Base {
  // new: completely replace the base class method
  // abstract: inheritors must implement the method
  public new abstract int GetInt();
}

public class Child : AbstractChild {
  // override: implement an abstract method
  public override int GetInt() {
    return 2;
  }
}

Base b = new Child();
Console.Out.WriteLine(b.GetInt());// prints 1

public abstract class Base {
  // virtual: method can be overridden
  public virtual int GetInt() {
    return 1;
  }
}

public abstract class AbstractChild : Base {
  // override the base class method
  // abstract: inheritors must implement this method
  public override abstract int GetInt();
}

public class Child : AbstractChild {
  // override: implement an abstract method
  public override int GetInt() {
    return 2;
  }
}

class Program {
  static void Main(string[] args) {
    Base c = new Child();
    Console.WriteLine(c.GetInt());
    Console.ReadLine();
  }
}

Maysam Mahfouzi wrote:

I didn't know that a method with override modifier can have no body.

public CardDetail MyCardDetail;

//constructor
public NewOrder()
{
    MyCardDetail = new CardDetail();
    MyCardDetail.CardFirstName = "Horace";
    MyCardDetail.CardLastName = "Horsecollar";
    MyCardDetail.CardNumber = "1ABC23";
}

using System;
using System.IO;
using System.Xml.Serialization;
using System.Data;
using System.Web;
using System.Collections;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.ComponentModel;
using ExampleforCodeProject;

namespace ExampleforCodeProject
{

    [WebService(Namespace = "http://MyXmlTest/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [ToolboxItem(false)]
    public class Order : System.Web.Services.WebService
    {

        [WebMethod]
        public NewOrder SerialiseOrder()
        {
            NewOrder order1 = new NewOrder();



            order1.AccountGroup = "11";
            order1.AccountNumber = "878";
            order1.Card.CardFirstName = "George";
            order1.Card.CardLastName = "Balden";
            order1.Card.CardNumber = "872947924793274";



            Stream stream = File.Open("C:\\test\\NewSoap.xml", FileMode.Create); //Create a file
            XmlSerializer sf = new XmlSerializer(typeof(NewOrder)); //
            sf.Serialize(stream, order1); //serialise
            stream.Close();
            return order1;
        }
    }
}

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using ExampleforCodeProject; 

namespace ExampleforCodeProject
{
    [Serializable]
    public class NewOrder
    {

        public NewOrder() { } //constructor
        ~NewOrder() { } //Destructor

        private string accountGroupfield;
        private string accountNumberfield;

        public string AccountGroup
        {
            get
            {
                return accountGroupfield;
            }
            set
            {
                accountGroupfield = value;
            }
        }

        public string AccountNumber
        {
            get
            {
                return accountNumberfield;
            }
            set
            {
                accountNumberfield = value;
            }
        }

        public CardDetail Card;

        [Serializable]
        public class CardDetail
        {

            private string cardFirstNamefield;
            private string cardLastNamefield;
            private string cardNumberfield;

            public string CardFirstName
            {
                get
                {
                    return cardFirstNamefield;
                }
                set
                {
                    cardFirstNamefield = value;
                }
            }

            public string CardLastName
            {
                get
                {
                    return cardLastNamefield;
                }
                set
                {
                    cardLastNamefield = value;
                }
            }

            public string CardNumber
            {
                get
                {
                    return cardNumberfield;
                }
                set
                {
                    cardNumberfield = value;
                }
            }
        }
    }
}