Lesson 25: Object-Oriented Programming

Master core OOP concepts in VB2019: encapsulation, inheritance, and polymorphism

Key Takeaway

Object-oriented programming (OOP) allows you to model real-world entities as software objects, making code more modular, reusable, and maintainable.

Object-oriented programming (OOP) is the foundation of Visual Basic 2019. In this lesson, we'll explore the three core OOP concepts: encapsulation, inheritance, and polymorphism. These concepts enable you to create more organized, reusable, and maintainable code.

Encapsulation

Bundling data and methods into self-contained modules

Inheritance

Creating new classes based on existing ones

Polymorphism

Using a single interface for different data types

Modularity

Building applications from reusable components

25.1 Core OOP Concepts

In order for a programming language to qualify as an object-oriented programming language, it must have three core technologies: encapsulation, inheritance and polymorphism.

Encapsulation

Encapsulation refers to the creation of self-contained modules that bind processing functions to the data. These user-defined data types are called classes. Each class contains data as well as a set of methods which manipulate the data. The data components of a class are called instance variables and one instance of a class is an object.

For example, in a library system, a class could be a member, and John and Sharon could be two instances (two objects) of the library class.

Inheritance

Classes are created according to hierarchies, and inheritance allows the structure and methods in one class to be passed down the hierarchy. That means less programming is required when adding functions to complex systems. If a step is added at the bottom of a hierarchy, then only the processing and data associated with that unique step needs to be added. Everything else about that step is inherited.

Polymorphism

Object-oriented programming allows procedures about objects to be created whose exact type is not known until runtime. For example, a screen cursor may change its shape from an arrow to a line depending on the program mode. The routine to move the cursor on the screen in response to mouse movement would be written for "cursor," and polymorphism allows that cursor to take on whatever shape is required at runtime. It also allows new shapes to be easily integrated.

25.2 Creating Classes in VB2019

Visual Basic 2019 allows users to write programs that break down into modules. These modules represent real-world objects and are knows as classes or types. An object can be created out of a class and it is known as an instance of the class. A class can also comprise subclass.

Figure 25.1: Adding a class in VB2019

To create a class, start Visual Basic 2019 as usual and choose Windows Applications. In the Visual Basic 2019 IDE, click on Project on the menu bar and select Add Class.

Figure 25.2: Add New Item dialog

Click on the Class item and the default class Class1.vb will appear as a new tab in a code window. Rename the class as MyClass.vb. Rename the form as MyFirstClass.vb.

Example: Creating a BMI Class

In the MyClass.vb window, create a new class MyClass1 with the following code:

MyClass.vb

Public Class MyClass1
    Public Function BMI(ByVal height As Single, ByVal weight As Single)
        ' Calculate BMI using metric formula
        BMI = Format((weight) / (height ^ 2), "0.00")
    End Function
End Class

Now you have created a class (an object) called MyClass1 with a method known as BMI that calculates Body Mass Index.

25.3 Using Classes in Your Application

In order to use the BMI class, insert a button into the form and add the following code to the button's click event:

Form1.vb

Private Sub BtnBMI_Click(sender As Object, e As EventArgs) Handles BtnBMI.Click
    ' Create an instance of the MyClass1
    Dim MyObject As Object
    Dim h, w As Single
    
    ' Instantiate the class
    MyObject = New MyClass1()
    
    ' Get user input
    h = InputBox("What is your height in meter")
    w = InputBox("What is your weight in kg")
    
    ' Call the BMI method and display result
    MessageBox.Show(MyObject.BMI(h, w), "Your BMI")
End Sub

When you run this program and click the button, the user will be presented with two input boxes to enter height and weight. The BMI value will then be shown in a message box.

Figure 25.3: Input height

Figure 25.4: Input weight

Figure 25.5: BMI calculation result

Lesson Summary

In this lesson, you've learned the fundamentals of object-oriented programming in VB2019:

OOP Concepts

Understand encapsulation, inheritance, and polymorphism

Class Creation

Create classes with properties and methods

Object Instantiation

Create objects from classes and use their methods

Practical Example

Implement a BMI calculator using OOP principles

Object-oriented programming is essential for creating scalable, maintainable applications. In the next lesson, we'll explore graphics programming in VB2019.

Next Lesson

Learn to create graphics in Lesson 26: Introduction to Graphics.

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