Tried to explain basics of polymorphism using easy example.

1. Circle
Rectangle
Triangle
Draw
Bhushan Mulmule
bhushan.mulmule@gmail.com
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2. Polymorphism is

3. Ability of different objects to respond same message
in different ways.
Circle
Rectangle
Triangle
Draw

4. We can achieve it using…

5. Inheritance, Upcasting and Late Binding
or
Abstract Class Implementation
or
Interface Implementation

6. Let us focus on first technique in this session
Polymorphism using Inheritance, Upcasting
and Late Binding
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7. Upcasting is holding derived class object
in base class reference

8. If we have this class hierarchy

9. we generally create objects…
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10. where references and objects are of same types
Shape s = new Shape();
s
shape
Circle c = new Circle();
c
Circle
Rectangle r = new Rectangle();
shape
Circle
r
Rectangle
Rectangle

11. As Circle and Rectangle are derived from Shape class.
You can also create object using upcasting…

12. where base class reference can hold
objects of derived class
Shape s = new Shape();
s
shape
shape
s = new Circle();
Circle
s = new Rectangle();
Rectangle
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13. Now let us try to understand Late Binding

14. Binding is connecting method Invocation to method
implementation
By default .NET use Early Binding …
Early binding is also referred as Static Binding or Compile Time Binding

15. If we have Draw() method in base class and also
redefined it in derived classes
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16. Redefining Draw() method
in Circle and Rectangle
Class hides the base class
implementation of Draw().
This is knows as
Shadowing.
Note: new keyword just confirms that you are
intentionally shadowing Draw() method in
derived class.

17. And we have created objects using upcasting
and invoked Draw() method

19. Then the output that we are expecting is…

20. Expected Output
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21. But What’s this?
Output is surprising…

22. Actual Output
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23. Why?
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24. Because by default .NET use early binding.
Compiler simply checks type of reference and bind it
accordingly.
Compiler doesn't care about type of object. Actually there are no objects in
memory at compile time

25. As s is of Shape type so all the three calls will get binded to
Draw() of Shape class irrespective of Object it is pointing to

26. What's the solution?
Is it possible to bind method call depending on object type instead
of reference type?

27. And here is the magic keyword
virtual
Call to virtual method gets resolved at runtime depending on actual
object type.

28. The virtual keyword marks method for late
or dynamic binding.
Virtual method has to be overridden in a
derived class using override keyword and
can be modified

29. Now Let us run same client code
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30. Will call Draw() of Shape
Will call Draw() of Circle
Will call Draw() of Rectangle

31. And yes this time output will be…

32. As expected.
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33. Polymorphism is
ability of different objects
to respond same message
In different ways

34. For Video visit
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35. Bhushan Mulmule
bhushan.mulmule@dotnetvideotutorial.com
www.dotnetvideotutorial.com