Visual Basic.NET How to Program (PDF)

226 Procedures Chapter 6
6.17 Procedure Overloading and Optional Arguments
Visual Basic provides several ways of allowing procedures to have variable sets of parameters.
Overloading allows the programmer to create multiple procedures with the same
name, but differing numbers and types of arguments. This allows the programmer to reduce
the complexity of the program and create a more flexible application. Procedures also can
receive optional arguments. Defining an argument as optional allows the calling procedure
to decide what arguments to pass. Optional arguments normally specify a default value that
is assigned to the parameter if the optional argument is not passed. Overloaded procedures
are generally more flexible than procedures with optional arguments. For instance, the programmer
can specify varying return types for overloaded procedures. However, optional
arguments present a simple way of specifying default values.
6.17.1 Procedure Overloading
By overloading, a programmer can define several procedures with the same name, as long
as these procedures have different sets of parameters (number of parameters, types of parameters
or order of the parameters). When an overloaded procedure is called, the compiler
selects the proper procedure by examining the number, types and order of the call’s arguments.
Often, procedure overloading is used to create several procedures with the same
name that perform similar tasks on different data types.
Good Programming Practice 6.6
The overloading of procedures that perform closely related tasks can make programs more
readable and understandable. 6.6
The program in Fig. 6.22 uses overloaded method Square to calculate the square of
both an Integer and a Double.
1 ' Fig. 6.22: Overload.vb
2 ' Using overloaded methods.
3
4 Public Class FrmOverload
5 Inherits System.Windows.Forms.Form
6
7 Friend WithEvents outputLabel As Label
8
9 ' Visual Studio .NET generated code
10
11 Private Sub FrmOverload_Load(ByVal sender As System.Object, _
12 ByVal e As System.EventArgs) Handles MyBase.Load
13
14 outputLabel.Text = "The square of Integer 7 is " & _
15 square(7) & vbCrLf & "The square of Double " & _
16 "7.5 is " & square(7.5)
17 End Sub ' FrmOverload_Load
18
19 Function Square(ByVal value As Integer) As Integer
20 Return Convert.ToInt32(value ^ 2)
21 End Function ' Square
Fig. Fig. 6.22 6.22 Overloaded methods (part 1 of 2).