Consider the following class:
<%@ Page Language="VB" %>
<html>
<head>
<script language="vb" type="text/vb" runat="server">
Friend Class Rectangle
Public Shared Length As Double
Public Shared Height As Double
Public Function CalculatePerimeter#()
Return (Length + Height) * 2
End Function
Public Function CalcaulteArea#()
Return Length * Height
End Function
End Class
</script>
<title>Exercise</title>
</head>
<body>
<%
REM Notice that a Rectangle variable is not declared
Rectangle.Height = 20.68
Rectangle.Length = 32.47
Response.Write("Rectangle Characteristics" & "<br />" & _
"Length:" & vbTab & Rectangle.Length & "<br />" & _
"Height:" & vbTab & Rectangle.Height)
%>
</body>
</html>
This would produce:
Like member variables, a method can be shared among
classes. In some cases, shared methods are more used than shared member
variables because a shared method allows performing an action on a
class without declaring an instance of that class. To create a shared method, type the Shared keyword
on the left of the Sub or the Function keyword. Here is an
example:
Here is an example:
<script language="vb" type="text/vb" runat="server">
Friend Class Rectangle
Shared Function CalculatePerimeter#()
Return (Length + Height) * 2
End Function
End Class
</script>
You can apply the access modifier on the method as we have
done so far. Here are examples:
<script language="vb" type="text/vb" runat="server">
Friend Class Rectangle
Public Shared Function CalculatePerimeter#()
End Function
Public Shared Function CalcaulteArea#()
End Function
End Class
</script>
Like a shared member variable, once a
method has been created as shared, it can be accessed directly from
anywhere. Remember that you would need to type the name of the class
before accessing the method. The name of the class allows you to
"qualify" the method. Here is an example:
<%@ Page Language="VB" %>
<html>
<head>
<script language="vb" type="text/vb" runat="server">
Friend Class Rectangle
Public Shared Length As Double
Public Shared Height As Double
Public Shared Function CalculatePerimeter#()
Return (Length + Height) * 2
End Function
Public Shared Function CalcaulteArea#()
Return Length * Height
End Function
End Class
</script>
<title>Exercise</title>
</head>
<body>
<%
REM Notice that a Rectangle variable is not declared
Rectangle.Height = 20.68
Rectangle.Length = 32.47
Response.Write("Rectangle Characteristics" & "<br />" & _
"Length:" & vbTab & vbTab & Rectangle.Length & "<br />" & _
"Height:" & vbTab & vbTab & Rectangle.Height & "<br />" & _
"Perimeter: " & vbTab & Rectangle.CalculatePerimeter#() & "<br />" & _
"Area: " & vbTab & vbTab & Rectangle.CalcaulteArea#())
%>
</body>
</html>
This would produce:
We have mentioned two techniques of accessing the members of
a class, one consisted of declaring a variable of the class, the other had to do
with Shared members. We know
already that the members of a class are made available to all other members of
the same class without being declared or qualified. Consider the following
class:
<script language="vb" type="text/vb" runat="server">
Public Class Triangle
Public Base As Double
Public Height As Double
Public Area As Double
Public Sub Create()
Dim Area As Double
Area = Base * Height / 2
End Sub
End Class
</script>
When the Area variable is used in the Display() method,
there are two variables available and named Area. It makes it confusing to know
what particular variable is being accessed. You can use a special member of a class that allows you to specify the member of a
class when accessing it. This member is called Me.
When using Me, you can access any member of a class within any method of the same
class. Here is an example:
<script language="vb" type="text/vb" runat="server">
Public Class Triangle
Public Base As Double
Public Height As Double
Public Area As Double
Public Sub Create()
Dim Area As Double
' Using "this" to access the members of this class
Me.Base = 24.55
Me.Height = 20.75
' You cannot use this to access Area because Area
' is not a member of this class
Area = Me.Base * Me.Height / 2
End Sub
End Class
</script>
There are rules you must follow when using Me:
|
The Shared Members of a Class
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