Overloading and Overriding in Visual Basic.NET 2005 - Multi-level method overriding in Visual Basic 2005 inheritance

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In the previous section, I covered the meaning of overriding.  In this section, I shall extend the same concept further to multi-level inheritance and overriding in Visual Basic 2005.

Let us redefine our classes as follows:

Public Class Parent

  Public Overridable Sub DispMsg()

    MessageBox.Show("From Parent")

  End Sub

End Class

 

Public Class Child

  Inherits Parent

  Public Overrides Sub DispMsg()

    MessageBox.Show("From child")

  End Sub

End Class

 

Public Class GrandChild

  Inherits Child

  Public Overrides Sub DispMsg()

    MessageBox.Show("From grand child")

  End Sub

End Class

If you observe the above code, I defined three classes with multi-level inheritance (child inherited from parent and grandchild inherited from child).  You can still see that the same "DispMsg" method is defined in all of the classes. 

If a method is defined with "overridable" in the parent, it can be overridden in child classes using "overrides."  If a class has a method already defined with "overrides," it is implicitly declared as "overridable" and we need not define both "overrides" and "overridable" at the same time.

To test the above code, simply create an object based on the "GrandChild" class and try to call "DispMsg" as shown:

Dim obj As New GrandChild

obj.DispMsg() 'displays "From grant child"

Even in this case, if you try to convert the "GrandChild" object to any of its parent or grandparent classes and access the "DispMsg" method, you will receive the same output.

In my next article, I shall introduce "shadows."  I hope you enjoyed the article and any suggestions, bugs, errors, enhancements etc. are highly appreciated at http://jagchat.spaces.live.com

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Comments On: Overloading and Overriding in Visual Basic.NET 2005

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