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Classes, modules and structures in VB.NET

Modules, classes and structures all look very similar in VB.NET, so it wouldn't be suprising to hear that they are often confused. This article will look at all of them and the difference between them.

Program structure

Modules, classes and structures are all part of program structure - they are used to seperate the program into more manageable chunks of code. They all serve individual purposes but can contain almost the same kind of data.

Class

A class is a way of storing variables (data) and methods. All code goes into a class of some kind. A class can have an access modifier applied to it so that it can be hidden or publicly exposed.

Within a class exist variables. They can be declared Public, Private, Protected or Friend. This limits the scope of the variable.The access modifier of the class defines the overall access modifier for all the variables and methods.

If a variable is declared Public in a Private class, it cannot be used elsewhere.

Methods also exist within a class. They too can be given an access modifier. They can be called by using the Call statement or by simply typing their path such as: Class.Method().

A class can be instantiated, meaning that it can be created as a new copy of the class (an instance of a class). Classes tend to work this way.

VB.NET
Public Class SampleClass
	'Code goes here
End Class
		

Module

A module is a very simple 'version' of a class. Modules are static, meaning that they do not change (hence why in the C family of languages the equivalent of a VB.NET module is a public static method). In this case, they are not instantiated. This is why Console Applications use modules. Modules can be seen as helper classes, meaning that the methods within it are used to support the main program. Because of the fact that modules are static, they may not be inherited.

Below is a sample of how a Console Application looks, note the fact that it is a module with an entry point (a place for the program to start running at) called Sub New().

VB.NET
Module Module1
	Sub Main()
		'Code goes here
	End Sub
End Module
		

Structures

Structures are stored in memory differently to classes but on the top they work similarly to classes. Their uses are limited but can be used to store smaller pieces of data, for instance a 3D point. The following is such an example:

VB.NET
Public Structure SampleStructure

	Public x As Integer
	Public y As Integer
	Public z As Integer

	Public Sub SampleMethod()
		'Code goes here
	End Sub

End Structure
		

Structures can be used for storing records similar to the way they are done in databases.

There is more on classes and structures here.

  • Write a program that uses structures that store information about a person. You may want to call this structure student.
  • Within the student, declare 3 fields: first_name, last_name and test_score.
  • Again within the structure, declare a method (subroutine) that will print the student's first name, last name and their test score to the display called display.
  • Produce an array of three student instances with different names and test scores in each of them.
  • Create a For Each loop that iterates the list and runs the display method for each student.
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