Polymorphism helps you to perform different functions by using the same methods. To elaborate, the implementation of a base class can be changed in the derived classes. Therefore, when two classes are derived from the same class, a method can be created with the same name in both the classes. Based on the task that needs to be performed, you can select the method.

You learned about the features of object-oriented programming language, such as abstraction, encapsulation, inheritance, and polymorphism. Now, have a look at the components of Visual Basic .NET.

Components of Visual Basic .NET

You have learned about the components of Visual C# .NET throughout this book.This appendix discusses the components of Visual Basic .NET. These components include variables, constants, operators, arrays, collections, procedures, arguments, and functions.

Variables

Applications deal mostly with different types of data, such as text or numeric. This data needs to be stored by an application for later use and for performing certain operations on the data. It also needs to be stored for performing certain operations, such as calculating totals. A programming language uses variables in order to store data. A temporary memory location is called a variable that has a name or a word to refer to and a data type to determine the kind of data it can hold.

Visual Basic .NET provides various data types that help in storing different kinds of data. In the following section, you will learn more about the data types.

Data Types

The kind of data that a variable can hold is referred to as a data type. Integer, Long, and Byte are some of the data types that are provided by Visual Basic .NET. Table B-1 lists the various data types of Visual Basic .NET.

Variable Initialization

A variable contains a value when it is declared. Consider the following example: By default, an Integer variable contains 0 and a Boolean variable stores False as the value.

To set a start value, you can initialize a variable. The following code explains the variable:

Dim int1 as Integer int1 = 20

An Integer variable, int1, is declared by the first statement, while the second statement initializes it to the value 20. In the earlier versions of Visual Basic, the initialization of variables was not allowed in the same line as their declarations. But now, Visual Basic .NET allows it.Therefore, the code can now be written as:

Dim int1 As Integer = 20

Variable Scope

The scope of a variable determines the part of the program or application that can use the variable. Consider an example. A variable can be used only within a particular block of code or the entire program. Based on its scope, a variable can be called local or module-level. You can also refer to the scope of a variable as its accessibility.

If a variable is declared inside a procedure, it can only be accessed within that procedure. The variable is then referred to as a local variable. At times, you need to use a variable across modules within an application or throughout the application. The variable is then referred to as module-level variables.The declaration section of the module declares these variables. Module-level variables can be further clas-

sified as private or public.

The modules that can be used within the module in which they are declared are known as private modules.These modules are declared only at the module-level. A private variable is declared in the following statements:

Private Dim int1 As Integer

or

Private int1 As Integer