Object-Oriented Programming

Object-Oriented Programming, or OOP, is a style of programming that organizes code around classes and objects. A class is a blueprint, while an object is an actual instance created from that blueprint. :contentReference[oaicite:3]{index=3}

This approach helps programmers build programs that are easier to understand, reuse, and maintain.

• Class → blueprint
• Object → instance created from a class
• Property → data belonging to an object
• Method → action performed by an object

Suppose you want to describe a student. A student has a name, an age, and a course. These are properties. A student can also perform actions, such as displaying information. These are methods.

Public Class Student
    Public Name As String
    Public Age As Integer
    Public Course As String

    Public Sub ShowInfo()
        MsgBox("Name: " & Name & vbCrLf &
               "Age: " & Age & vbCrLf &
               "Course: " & Course)
    End Sub
End Class

The code above defines a class named Student.

After defining a class, you can create an object from it by using the New keyword.

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim s1 As New Student

    s1.Name = "John Tan"
    s1.Age = 20
    s1.Course = "Computer Science"

    s1.ShowInfo()
End Sub

Here, s1 is an object created from the Student class.

A property stores data, while a method performs an action. In modern OOP practice, properties are often preferred over public fields because they allow better control and validation. :contentReference[oaicite:4]{index=4}

Public Class Employee
    Private _name As String

    Public Property Name As String
        Get
            Return _name
        End Get
        Set(value As String)
            _name = value
        End Set
    End Property
End Class

Using properties makes your code more structured and flexible.

A constructor is a special procedure that runs automatically when an object is created. In Visual Basic, the constructor is written using Sub New. :contentReference[oaicite:5]{index=5}

Public Class Student
    Public Name As String
    Public Age As Integer

    Public Sub New(studentName As String, studentAge As Integer)
        Name = studentName
        Age = studentAge
    End Sub
End Class

Dim s1 As New Student("Alice", 19)

This makes object creation easier and more organized.

Inheritance allows one class to reuse the features of another class. The new class is called the child class, while the original class is called the parent class. In Visual Basic, inheritance uses the Inherits keyword. :contentReference[oaicite:6]{index=6}

Public Class Person
    Public Name As String

    Public Sub ShowName()
        MsgBox("Name: " & Name)
    End Sub
End Class

Public Class Teacher
    Inherits Person

    Public Subject As String
End Class

Here, the Teacher class inherits the Name property and the ShowName() method from the Person class.

Polymorphism means the same method name can behave differently in different classes. In Visual Basic, this is commonly done with Overridable and Overrides. :contentReference[oaicite:7]{index=7}

Public Class Animal
    Public Overridable Sub MakeSound()
        MsgBox("Animal sound")
    End Sub
End Class

Public Class Dog
    Inherits Animal

    Public Overrides Sub MakeSound()
        MsgBox("Woof!")
    End Sub
End Class

This allows child classes to provide their own behavior while keeping the same method name.