Objectives. After completing this topic, the students will: Understand of the concept of polymorphism Know on How to implement 2 types of polymorphism

Transcription

1 Polymorphism

2 Objectives After completing this topic, the students will: Understand of the concept of polymorphism Know on How to implement 2 types of polymorphism

3 Definition Polymorphism provides the ability to vary the implementation of a method or property

4 Polymorphism concepts With polymorphism, the same method or property can perform different actions depending on the runtime type of the instance that invokes it. ( Therefore the polymorphism enables us to "program in general" rather than "program in specific".

5 Polymorphism concepts Polymorphism happens in the inheritance hierarchical, hence when can said that the different implementation of a method or property in a specific group of classes.

6 Abstraction Abstraction means to create a model of an object, for the purpose of determining the characteristic (properties) and behaviors (methods) of the object.

7 Abstraction An abstract class is a class that never has an instance. In contras, a concrete class is a class that has one or more instances.

8 Implementation The form of polymorphism can be implemented in two ways: Overload and Override

9 Override Override refers to a method that has the same signature (name and parameter list) as a method in its base class. The method in derived class take precedence or overrides the identically name method in the base class. In order to allow a method in a base class being overridden, it must be declared as "Overridable"

10 Override Car Sedan Pick-up

11 Override Public Class Car Protected ID As String Protected ColourValue As String Public Property Colour() As String Get Return ColourValue End Get Set(ByVal value As String) ColourValue = value End Set End Property Public Overridable Sub Print() Console.WriteLine(ID) End Sub End Class

12 Override Public Class Sedan Inherits Car Private speed as double Public Overrides Sub Print() Console.WriteLine(ID) Console.WriteLine(speed) End Sub End Class

13 Override Public Class PickUp Inherits Car Private tonnage as double Public Overrides Sub Print() Console.WriteLine(ID) Console.WriteLine(tonnage) End Sub End Class

14 Overload Overload means the methods in different classes in a group of classes from an inheritance hierarchical have the same name but different signature

15 Overload

16 Overload

17 Overload

18 Overload Public Class Car Private CarSpeedValue As Integer Public Property CarSpeed() As Integer Get Return CarSpeedValue End Get Set(ByVal value As Integer) CarSpeedValue = value End Set End Property

19 Overload Public Overloads Sub IncreaseSpeed() CarSpeed += 1 End Sub Public Overloads Sub IncreaseSpeed(ByVal AmountToIncrease As Integer) CarSpeed += AmountToIncrease End Sub End Class

20 Overload Public Class SpeedPanel Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click If TextBox1.Text <> "" Then Dim MyCar As New Car MyCar.CarSpeed = Val(TextBox1.Text) If TextBox2.Text <> "" Then MyCar.IncreaseSpeed(Val(TextBox2.Text)) Else MyCar.IncreaseSpeed() End If TextBox1.Text = Str(MyCar.CarSpeed)

21 Overload End If End Sub Private Sub SpeedPanel_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load End Sub End Class

22 References Visual Basic 2005 How To Program, Deitel, Pearsons, 2006, ISBN Object Oriented Programming in VB.Net, Alistair McMonnies, Addison-Wesley, 2003, ISBN / s/class.html

23 Dr. Ir. Muhammad Ikhwan Jambak, MEng