VB.NET Interfaces

Question

I am not quite clear as to why or when to use Interfaces. Can someone post a complete, simple and small example of an Interface using VB.NET in a Console Application. How is it

Answer 1

Consider this simple interface:

Public Interface IWeightedValue
    Public ReadOnly Property Weight As Double
    Public ReadOnly Property Value As Double
End Interface

Without even writing any more code, I can start dealing with this concept in other parts of my code. For instance:

Public Function GetWeightedAverage(ByVal points As IEnumerable(Of IWeightedValue)) As Double
    Dim totalWeight As Double = 0.0
    Dim totalWeightedValue As Double = 0.0

    For Each point As IWeightedValue in points
        totalWeight += point.Weight
        totalWeightedValue += (point.Weight * point.Value)
    Next

    Return totalWeightedValue / totalWeight
End Function

And voila -- now for any class I write, if I just make it implement IWeightedValue then I can calculate the weighted average for a collection of instances of this class.