For example, in the following
code
Interface IUIControl
Sub Paint()
End Interface
IUIControl has only one member, the method Paint, and it uses only a Sub statement to
declare it, without providing a method body or an End Sub statement.
Interfaces, like classes, default to Friend accessibility in a namespace, but you can also
declare them Public.Within classes, modules, interfaces, and structures, they default to Public,
but they can also be Friend, Protected, or Private. Interface members are implicitly Public and
may not have access modifiers.
nNote By convention, interface names start with I.
Let??™s code a trivial interface to get familiar with how you declare and use interfaces:
Interface ITrivial
End Interface
Class A
Implements ITrivial
End Class
CHAPTER 6 n INTERFACES 98
Class B
Implements ITrivial
End Class
Public Class EntryPoint
Shared Sub Main()
Dim ca As ITrivial = New A
Dim cb As ITrivial = New B
End Sub
End Class
ITrivial is as trivial as an interface can get. Class A and Class B both implement it, but
trivially, since it has no members to implement. However, by implementing ITrivial, you can
store instances of both Class A and Class B in ITrivial variables. This is an example of how
interfaces support polymorphism.
Pages:
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189