Applying Polymorphism in VB.Net
This article inspires you how to take advantage of polymorphism in VB.Net. This article stresses that polymorphism can lead to nightmares and headaches. And this problem can be solved with the VB.Net keyword called My Class.
Notice the code:
Class Parent
Public Overridable Sub p1()
Console.Write("Parent.p1")
End Sub
Public Sub p2()
MyClass.p1()
'Implementing keyword MyClass here tells all derived classes to refer to the base / abstract class wherein the keyword MyClass appears
End Sub
End Class
Class Child
Inherits Parent
Public Overrides Sub p1()
Console.Write("Child.p1")
MyBase.p2()
End Sub
End Class
Sub Main()
Dim p As Parent
Dim c As Child
p = New Parent()
p.p1() 'OK
p.p2() 'OK
p = New Child()
p.p1() 'stack overflow error is prevented
My class has to apply here. If it is not so, a stack overflow error is shown.
Parent.p2() calls Parent.p1()
Parent.p1() is polymorphic because it can be overridden
Child.p1() overrides Parent.p1() so any calls to Parent.p1() will actually call Child.p1() if you have an instance of class Child
Child.p1() calls MyBase.p2()
MyBase.p2() is actually Parent.p2()
The drawback happens when you have an instance of class Child and call procedures p1 and p2. Calling p1 produces the following implementation flow:
Child.p1 -> Parent.p2 -> Child.p1 -> Parent.p2 -> Child.p1 -> etc.
And the cycle repeats until we have no stack space left. Calling p2 produces the following execution flow:
Child.p2 -> Child.p1 -> Parent.p2 -> Child.p1 -> Parent.p2 -> Child.p1 -> etc.
Applying the keyword MyClass in the base class tells all derived classes to use the method in the base class itself and, therefore, a stack overflow error is prevented.
p.p2() 'stack overflow error is prevented
c = New Child()
c.p1() 'stack overflow error is prevented
c.p2() 'stack overflow error is prevented
End Sub
Have a nice coding!
