In Visual Basic, objects can have one or more interfaces. All objects have a primary, or native, interface, which is composed of any methods, properties, events, or member variables declared using the Public keyword. You can also have objects implement secondary interfaces in addition to their native interface by using the Implements keyword.
The native interface on any class is composed of all the methods, properties, events, and even variables that are declared as anything other than Private. Though this is nothing new, do a quick review of what is included in the native interface to set the stage for discussing secondary interfaces. To include a method as part of your interface, you can simply declare a Public routine:
Public Sub AMethod() End Sub
Notice that there is no code in this routine. Any code would be implementation and is not part of the interface. Only the declaration of the method is important when discussing interfaces. This can seem confusing at first, but it is an important distinction, as the separation of the interface from its implementation is at the very core of object-oriented programming and design.
Because this method is declared as Public, it is available to any code outside the class, including other applications that may make use of the assembly. If the method has a property, then you can declare it as part of the interface by using the Property keyword:
Public Property AProperty() As String End Property
You can ...