public class BaseClass
    {
        public string m_Name = "BaseClass";

        public void RealName()
        {
            Console.WriteLine(m_Name);
        }

        public virtual void VirtualName()
        {
            Console.WriteLine(m_Name);
        }
    }

    public class DerivedClass : BaseClass
    {
        public string m_Name = "DerivedClass";

        public void RealName()
        {
            Console.WriteLine(m_Name);
        }

        public override void VirtualName()
        {
            Console.WriteLine(m_Name);
        }
    }

    public class Class2
    {
        [STAThread]
        static void Main(string[] args)
        {
            BaseClass lBaseclass = new DerivedClass();
            lBaseclass.RealName();//return :  BaseClass 
            lBaseclass.VirtualName();//return :  DerivedClass
            Console.WriteLine("-----------------------");

            DerivedClass lDerivedClass = (DerivedClass)lBaseclass;
            lDerivedClass.RealName();//return :  DerivedClass
            lDerivedClass.VirtualName();//return :  DerivedClass
            Console.WriteLine("-----------------------");

            lBaseclass.m_Name = "ModifyByBase";
            lBaseclass.RealName();//return :  ModifyByBase
            lBaseclass.VirtualName();//return :  DerivedClass
            Console.WriteLine("-----------------------");

            lDerivedClass.m_Name = "ModifyByDerived";
            lDerivedClass.RealName();//return :  ModifyByDerived
            lDerivedClass.VirtualName();//return :  ModifyByDerived
            Console.WriteLine("-----------------------");


            lDerivedClass = new DerivedClass();
            ((BaseClass)lDerivedClass).RealName();//return :  BaseClass
            ((BaseClass)lDerivedClass).VirtualName(); //return :  DerivedClass            

            Console.ReadLine();
        }    

    }