topik 4.2 inheritance polymorphism

7/30/2019 Topik 4.2 Inheritance Polymorphism

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F5227VISUAL BASIC .NET PROGRAMMING

Topic 4.2 :

Apply Inheritance And Polymorphism


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Course Learning Outcome (CLO) Upon completion of this course, students should be able to :

1. Create a simpe VB.NET based application based on the

Windows Application template.

2. Describe on essential terminology including memory,data types and graphical user interface.

3. Apply object oriented programming techniques to

create classes, add methods and add properties.

4. create a simple VB.NET

based Web forms applicationthat uses an XML Web Service and manipulate data in

database by using Microsoft ADO.NET.


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Course Learning Outcome:

Topic 4.0

1. Apply object oriented programming techniques to

create classes, add methods and add properties. (CLO3)


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Topic 4.0

Topic 4.1 : Use Classes, Object and Methods

Topic 4.2 : Apply Inheritance And

Polymorphism

Topic 4.3 : Construct Program Using String

Methods

Topic 4.4 : Understand the concepts ofException Handling


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Inheritance

A key feature of OOP is reusability.

It's always time saving and useful if we can

reuse something that already exists rather

than trying to create the same thing again and

again.

Reusing the class that is tested, debugged and

used many times can save us time and effort

of developing and testing it again


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The old class is called the base class and the

new class is called derived class.

The derived class inherits some or everything

of the base class.

In Visual Basic we use the Inherits keyword to

inherit one class from other.


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Once a class has been written and tested, it

can be used by other programs to suit the

program's requirement.

This is done by creating a new class from an

existing class.

The process of deriving a new class from an

existing class is called Inheritance.


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Inheritance

Public Class One

---

---

End Class

Public Class Two

Inherits One---

---

End Class


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Inheritance

Using Inheritance we can use the variables,

methods, properties, etc, from the base class

and add more functionality to it in the derived

class.


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Imports System.Console

Module Module1

Sub Main()

Dim ss As New Two()

WriteLine(ss.sum())Read()

End Sub

End Module

Public Class One

'base class

Public i As Integer = 10Public j As Integer = 20

Public Function add() As Integer

Return i + j

End Function

End Class

Public Class Two

Inherits One

'derived class. class two inherited from class one

Public k As Integer = 100

Public Function sum() As Integer

'using the variables, function from base class and adding more functionality

Return i + j + kEnd Function


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Output


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Polymorphism

MSDN (Microsoft Developer Network)

explanation,

"Polymorphism is the ability for classes to

provide different implementations of methods

that are called by the same name.

Polymorphism allows a method of a class to be

called without regard to what specificimplementation it provides."
http://www.programmersheaven.com/2/Les_VBNET_5_p4http://www.programmersheaven.com/2/Les_VBNET_5_p4


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Polymorphism

Polymorphism is one of the crucial features of

OOP. It means "one name, multiple forms".

It is also called as Overloading which means

the use of same thing for different purposes.


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Polymorphism

Using Polymorphism we can create as many

functions we want with one function name

but with different argument list.


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Polymorphism

The function performs different operations

based on the argument list in the function call.

The exact function to be invoked will be

determined by checking the type and number

of arguments in the function.


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ExampleModule Module1Sub Main()

Dim two As New One()

WriteLine(two.add(10))

'calls the function with one argument

WriteLine(two.add(10, 20))

'calls the function with two arguments

WriteLine(two.add(10, 20, 30))

'calls the function with three arguments

Read()

End Sub

End Module

Public Class One

Public i, j, k As Integer

Public Function add(ByVal i As Integer) As Integer

'function with one argument

Return i

End Function

Public Function add(ByVal i As Integer, ByVal j As Integer) As Integer

'function with two arguments

Return i + j

End Function

Public Function add(ByVal i As Integer, ByVal j As Integer, ByVal k As Integer) As Integer

'function with three arguments

Return i + j + k

End Function

End Class


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Output


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Overriding the method

The Overridable and the Overrides keywords

Overridable allow a method to be overridden

and be used polymorphically.

Overrides is overriding the virtual method in

the base class.

topik 4.2 inheritance polymorphism

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