Polymorphism/Serialization DataContractSerializer (C#)

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.Serialization;
using System.IO;

namespace Polymorphism
{
    class Program
    {
        static int Main(string[] args)
        {
            // Create some objects
            DrawingObject[] dObj = new DrawingObject[4];

            dObj[0] = new Line(100,100);
            dObj[1] = new Circle(50,10,10);
            dObj[2] = new Square(10,10,20,20);
            dObj[3] = new DrawingObject();

            foreach (DrawingObject drawObj in dObj)
            {
                switch (drawObj.GetType().Name)
                {
                    case "Line":
                        Console.WriteLine (string.Format("I'm a {0}", drawObj.Draw()) );
                        Line line = (Line)drawObj;
                        break;
                    case "Circle":
                        Console.WriteLine (string.Format("I'm a {0}", drawObj.Draw()) );
                        Circle circle = (Circle)drawObj;
                        break;
                    case "Square":
                        Console.WriteLine (string.Format("I'm a {0}", drawObj.Draw()) );
                        Square square = (Square)drawObj;
                        break;
                    default:
                        Console.WriteLine (string.Format("I'm just a {0}", drawObj.Draw()) );
                        break;
                }
                drawObj.Draw();
            }

            // Serialize
            Serialize(dObj);

            List<DrawingObject> deserializedList = new List<DrawingObject>();
            // deserialize to a generic list
            deserializedList = Deserialize<List<DrawingObject>>();

            foreach (DrawingObject DrawingObject in deserializedList)
            {
                switch (DrawingObject.GetType().Name)
                {
                    case "Line":
                        Console.WriteLine (string.Format("I'm a {0}", DrawingObject.Draw()) );
                        Line line = (Line)DrawingObject;
                        break;
                    case "Circle":
                        Console.WriteLine (string.Format("I'm a {0}", DrawingObject.Draw()) );
                        Circle circle = (Circle)DrawingObject;
                        break;
                    case "Square":
                        Console.WriteLine (string.Format("I'm a {0}", DrawingObject.Draw()) );
                        Square square = (Square)DrawingObject;
                        break;
                    default:
                        Console.WriteLine (string.Format("I'm just a {0}", DrawingObject.Draw()) );
                        break;
                }
            }

            return 0;
        }

        public static void Serialize<T>(T data)
        {
            try // try to serialize the collection to a file
            {
                using (Stream  stream = File.Open("data.xml", FileMode.Create))
                {
                    // create DataContractSerializer
                    DataContractSerializer serializer = new DataContractSerializer(typeof (T));
                    // serialize the collection (EmployeeList1) to file (stream)
                    serializer.WriteObject(stream, data);
                }
            }
            catch (IOException)
            {
            }
        }

        public static T Deserialize<T>() where T : new()
        {
            // Create an instance of T
            T ReturnListOfT = CreateInstance<T>();

            // Try to Deserialize from file stream
            try
            {
                using (Stream stream = File.Open("data.xml", FileMode.Open))
                {
                    // create DataContractSerializer
                    DataContractSerializer serializer = new DataContractSerializer(typeof (T));
                    // deserialize the collection (Employee) from file (stream)
                    ReturnListOfT = (T)serializer.ReadObject(stream);
                }
            }
            catch (IOException)
            {
            }

            return (T)ReturnListOfT;
        }

        // function to create instance of T
        public static T CreateInstance<T>() where T : new()
        {
            return (T)Activator.CreateInstance(typeof(T));
        }
    }

    [KnownType(typeof(Line))]
    [KnownType(typeof(Circle))]
    [KnownType(typeof(Square))]
    [DataContract]
    class DrawingObject
    {
        public virtual string Draw()
        {
            return "generic drawing object.";
        }
    }

    [DataContract]
    class Square : DrawingObject
    {
        public override string Draw()
        {
            return "Square.";
        }

        public Square()
        {
        }

        public Square(int x1, int y1, int x2, int y2)
        {
            X1 = x1;
            Y1 = y1;
            X2 = x2;
            Y2 = y2;
        }

        [DataMember]
        public int X1 { get; set; }
        [DataMember]
        public int Y1 { get; set; }

        [DataMember]
        public int X2 { get; set; }
        [DataMember]
        public int Y2 { get; set; }
    }

    [DataContract]
    class Line : DrawingObject
    {
        public override string Draw()
        {
            return "Line.";
        }

        public Line()
        {
        }

        public Line(int x, int y)
        {
            this.X = x;
            this.Y = y;
        }

        [DataMember]
        public int X { get; set; }
        [DataMember]
        public int Y { get; set; }
    }

    [DataContract]
    class Circle : DrawingObject
    {
        public override string Draw()
        {
            return "Circle.";
        }

        public Circle()
        {
        }

        public Circle(int radius, int x, int y)
        {
            this.Radius = radius;
            this.X = x;
            this.Y = y;
        }

        [DataMember]
        public int Radius { get; set; }
        [DataMember]
        public int X { get; set; }
        [DataMember]
        public int Y { get; set; }
    }
}