C#

public partial class Form1 : Form
   {
       Rectangle SelectionRectangle = new Rectangle();
       string SelectedShape = "None";

       public Form1()
       {
           InitializeComponent();
       }

       private void Form1_MouseDown(object sender, MouseEventArgs e)
       {
           // If the current selected shape is 'Ellipse', then set the selection
           // rectangle's top-left position to mouse co-ordinates and set the width and
           // height to zero
           if (SelectedShape == "Ellipse")
           {
               SelectionRectangle.Width = 0;
               SelectionRectangle.Height = 0;
               SelectionRectangle.X = e.X;
               SelectionRectangle.Y = e.Y;
           }
       }

       private void Form1_MouseMove(object sender, MouseEventArgs e)
       {
           // If the mouse left button the pressed and the mouse is dragged, then capture
           // the mouse co-ordinates and resize the rectangle
           if (e.Button == MouseButtons.Left)
           {
               SelectionRectangle.Width = e.X - SelectionRectangle.Left; // EndPoint.X - StartPoint.Y;
               SelectionRectangle.Height = e.Y - SelectionRectangle.Top; // EndPoint.Y - StartPoint.Y;
               // ask Windows to redraw the form background
               Invalidate();
               Update();
           }
       }

       private void Form1_MouseUp(object sender, MouseEventArgs e)
       {
           // Capture the mouse position only if the current selected shape is 'Rectangle'
           // Else ignore
           if (SelectedShape == "Ellipse")
           {
               SelectionRectangle.Width = e.X - SelectionRectangle.Left; //EndPoint.X - StartPoint.X;
               SelectionRectangle.Height = e.Y - SelectionRectangle.Top; //EndPoint.Y - StartPoint.Y;
               Invalidate();
               Update();
           }

       }

       // Click 'Button2' to start drawing the ellipse
       private void button2_Click(object sender, EventArgs e)
       {
           SelectedShape = "Ellipse";
       }

       // Click 'Button2' to stop drawing the ellipse
       private void button1_Click(object sender, EventArgs e)
       {
           SelectedShape = "None";
       }

       private void Form1_Paint(object sender, PaintEventArgs e)
       {
           if ((SelectedShape == "Ellipse") && (SelectionRectangle != null))
           {
               Graphics g = e.Graphics;
               g.DrawEllipse(Pens.Black, SelectionRectangle);
               // If you do not want to draw the bounding rectangle, just comment out
               // the next line
               g.DrawRectangle(Pens.Gray, SelectionRectangle);
           }
       }

  public class Shape<br />
   {<br />
      String ShapeName ; // 'Line','Circle','Rectangle' etc.<br />
   }<br />
<br />
   public class Line : Shape<br />
   {<br />
      Point StartPoint;<br />
      Point EndPoint;<br />
<br />
      public Line() : base()<br />
      {<br />
         ShapeName = "Line";<br />
         .<br />
         .<br />
         .<br />
      }<br />
   }<br />
<br />
   public class Circle : Shape<br />
   {<br />
      Point Centre;<br />
      int Radius;<br />
<br />
      public Circle()<br />
      {<br />
         ShapeName = "Circle";<br />
         Radius = 0;<br />
         Centre = new Point(0,0); // some default location<br />
      }<br />
   }<br />
<br />
   ArrayList ShapeList = new ArrayList();

public interface IDataLayer {
 void DoSomething(string firstName, string lastName);
}

public interface IDataLayerFactory {
 IDataLayer Generate();
}

public class BusinessLayer {
 private IDataLayerFactory dataLayerFactory;

 protected BusinessLayer() {
  dataLayerFactory = null;
 }

 public BusinesLayer(IDataLayerFactory pDataLayerFactory) {
  dataLayerFactory = pDataLayerFactory;
 }

 public int Method1(string firstName, string lastName) {
  return dataLayerFactor.Generate().DoSomething(firstName, lastName);
 }

}

public class BusinessLayer {
 private IDataLayer dataLayer;

 protected BusinessLayer() {
  dataLayer = null;
 }

 public BusinesLayer(IDataLayer pDataLayer) {
  dataLayer = pDataLayer;
 }

 public int Method1(string firstName, string lastName) {
  return dataLayer.DoSomething(firstName, lastName);
 }

}

class ASpecificDataLayer : IDataLayer {
 public void DoSomething(string firstName, string lastName) {
  // implementation goes here
 }
};

class ASpecificDataLayerFactory : IDataLayerFactory {
 public IDataLayer Generate() {
  return new ASpecificDataLayer();
 }
};