Visual Basic.NET How to Program (PDF)

360 Object-Oriented Programming: Inheritance Chapter 9
72 ' calculate CCircle diameter
73 Public Function Diameter() As Double
74 Return mRadius * 2
75 End Function ' Diameter
76
77 ' calculate CCircle circumference
78 Public Function Circumference() As Double
79 Return Math.PI * Diameter()
80 End Function ' Circumference
81
82 ' calculate CCircle area
83 Public Function Area() As Double
84 Return Math.PI * mRadius ^ 2
85 End Function ' Area
86
87 ' return String representation of CCircle
88 Public Overrides Function ToString() As String
89 Return "Center = " & "[" & mX & ", " & mY & "]" & _
90 "; Radius = " & mRadius
91 End Function ' ToString
92
93 End Class ' CCircle
Fig. 9.6 CCircle class contains an x-y coordinate and a radius (part 3 of 3).
Module modCircleTest (Fig. 9.7) tests class CCircle. Line 12 instantiates an
object of class CCircle, assigning 37 as the x-coordinate value, 43 as the y-coordinate
value and 2.5 as the radius value. Lines 15–17 use properties X, Y and Radius to retrieve
these values, then concatenate the values to String output. Lines 20–22 use
CCircle’s X, Y and Radius properties to change the x-y coordinate pair value and radius
value, respectively. Property Radius ensures that member variable mRadius cannot be
assigned a negative value. Line 27 calls CCircle’s ToString method to obtain the
CCircle’s String representation, and lines 31–38 call CCircle’s Diameter, Circumference
and Area methods.
After writing all the code for class CCircle (Fig. 9.6), note that a major portion of
the code in this class is similar, if not identical, to much of the code in class CPoint. For
example, the declaration in CCircle of Private variables mX and mY and properties X
and Y are identical to those of class CPoint. In addition, the class CCircle constructors
and method ToString are almost identical to those of class CPoint, except that they
also supply mRadius information. In fact, the only other additions to class CCircle are
Private member variable mRadius, property Radius and methods Diameter,
Circumference and Area.
1 ' Fig. 9.7: CircleTest.vb
2 ' Testing class CCircle.
3
4 Imports System.Windows.Forms
5
Fig. 9.7 modCircleTest demonstrates class CCircle functionality
(part 1 of 2).