Visual Basic.NET How to Program (PDF)

Chapter 8 Object-Based Programming 333
11
12 ' constructor of class CCircleConstants
13 Public Sub New(ByVal radiusValue As Integer)
14 RADIUS = radiusValue
15 End Sub ' New
16
17 End Class ' CCircleConstants
Fig. 8.15 Constants used in class CCircleConstants (part 2 of 2).
Module modConstAndReadOnly (Fig. 8.16) illustrates the use of Const and
ReadOnly values. Lines 9–11 use class Random to generate a random Integer
between 1–20 that corresponds to a circle’s radius. Line 11 passes this value to the CCircleConstant
constructor to instantiate a CCircleConstant object. Line 13 then
accesses the ReadOnly variable mRadius through a reference to its class instance. Lines
15–17 compute the circle’s circumference and assign the value to String output. This
calculation employs the Const member PI, which we access in line 17 through its
Shared class reference. Lines 19–20 output the radius and circumference values to a
MessageBox.
1 ' Fig. 8.16: ConstAndReadOnly.vb
2 ' Demonstrates Const and ReadOnly members.
3
4 Imports System.Windows.Forms
5
6 Module modConstAndReadOnly
7
8 Sub Main()
9 Dim random As Random = New Random()
10 Dim circle As CCircleConstants = _
11 New CCircleConstants(random.Next(1, 20))
12
13 Dim radius As String = Convert.ToString(circle.RADIUS)
14
15 Dim output As String = "Radius = " & radius & vbCrLf _
16 & "Circumference = " + String.Format("{0:N3}", _
17 circle.RADIUS * 2 * CCircleConstants.PI)
18
19 MessageBox.Show(output, "Circumference", _
20 MessageBoxButtons.OK, MessageBoxIcon.Information)
21 End Sub ' Main
22
23 End Module ' modConstAndReadOnly
Fig. 8.16 Const and ReadOnly class member demonstration.