C#

Member 13299953 wrote:

My Understanding : The statement new Rectangle(); creates an object of type Rectangle in the memory and its reference is stored in object s of type Shape. So the object s should have access to variable num defined in rectangle class. Please make me understand this concept why we can’t access num variable from Object of type Shape.

public class Shape
    {
    public virtual void Draw()
        {
        Console.WriteLine("Drawing in Shape");
        }
    }
public class Rectangle : Shape
    {
    public int Ratio { get; set; }
    public override void Draw()
        {
        Console.WriteLine("Drawing in Rectangle");
        }
    }
public class Circle : Shape
    {
    public int Radius { get; set; }
    public override void Draw()
        {
        Console.WriteLine("Drawing in Circle");
        }
    }

Shape s = new Rectangle();
s.Draw();

Drawing in Rectangle

Shape s2 = new Circle();
s2.Draw();

Drawing in Circle

Console.Writeline("{0}", s.Ratio);

Console.Writeline("{0}", s.Radius);

Rectangle r = new Rectangle();
Circle c = new Circle();
Shape s = r;
s.Draw();
s = c;
s.Draw();
Console.WriteLine("{0}", r.Ratio);
Console.WriteLine("{0}", c.Radius);

public abstract class Shape
{
    public virtual void Draw(string txt = "Shape")  // Note 0
    {
        Console.WriteLine(txt);
    }
}

public class Rect : Shape
{
    public string Name = "Rect";

    public int Ratio { get; set; }

    public void Draw(String txt = "Rect")
    {
        base.Draw(txt);
    }
}

public class Circle : Shape
{
    public string Name = "Circle";

    public int Radius { get; set; }

    public void Draw(String txt = "Circle")
    {
        base.Draw(txt);
    }
}

// error: cannot create an instance of an abstract class
// Shape newShape = new Shape();

Rect newRectangle = new Rect();
Circle newCircle = new Circle();

newRectangle.Draw();
newCircle.Draw();

Shape shapeAsRectangle = newRectangle;  // Note 1
Shape shapeAsCircle = newCircle;

shapeAsRectangle.Draw();
shapeAsCircle.Draw();

Rect rectBackFromShape = shapeAsRectangle as Rect;  // Note 2
Circle rectBackFromCircle = shapeAsCircle as Circle;

rectBackFromShape.Draw();
rectBackFromCircle.Draw();

Console.WriteLine(newRectangle == shapeAsRectangle);   // true
Console.WriteLine(newCircle == shapeAsCircle);         // true
Console.WriteLine(newRectangle == rectBackFromShape);  // true
Console.WriteLine(newCircle == rectBackFromCircle);    // true

Quote:

Shape s = new Rectangle();

Gerry Schmitz wrote:

Shape rectShape = rect as Shape;

Quote:

No, it won't

Quote:

Because a form displayed as a dialog box is hidden instead of closed, you must call the Dispose method of the form when the form is no longer needed by your application.