References in VB.NET

Question

Somewhat unclear to me are references (pointers?) to classes in VB.NET. The question I am about to ask can be answered by a little bit of testing, but I was wondering if anybody could post a decent explanation (or links, too).

If you create a class:

Public Class ReferenceClass

    Private myBooleanValue As Boolean = False
    Public Property BooleanValue As Boolean
        Get
            Return myBooleanValue
        End Get
        Set(value As Boolean)
            myBooleanValue = value
        End Set
    End Property

End Class

And then a class which actually uses this class as a property:

Public Class UsingClass

     Private myReference As ReferenceClass
     Public Property Reference As ReferenceClass
        Get
             return myReference
         End Get
         Set(value As ReferenceClass)
             myReference = value
         End Set
     End Property

     Public Sub New(ByVal Reference As ReferenceClass)
         myReference = Reference
     End Sub

End Class

And then use it like this:

Public Class RuntimeOrSomething

     Public Shared myReference As ReferenceClass
     Public Shared ReadOnly Property Reference As ReferenceClass
         Get
             If myReference Is Nothing Then myReference = new ReferenceClass()
             return myReference
         End Get
     End Property

     Public Shared Function BooleanCheck() As Boolean
         Reference.BooleanValue = True
         Dim tempClass As New UsingClass(Reference)
         tempClass.Reference.BooleanValue = False

         Return (tempClass.Reference.BooleanValue = Reference.BooleanValue)
     End Sub

     Public Shared Sub DoNothing()
          Reference.BooleanValue = True
          Dim someBoolean As Boolean = BooleanCheck

          ' Now Reference.Booleanvalue is "False"
     End Sub

End Class

Now the function BooleanCheck will always return true, even though the reference is passed to the new class UsingClass "by value", not by reference. So a copy of the class is not made, but the local variable myReference in UsingClass still references/points to the property Reference in RuntimeOrSomething.

How can this be explained elegantly?

Answer 1

A reference points to an instance of an object, it is not an instance of an object. Making a copy of the directions to the object does not create another object, it creates another reference that also points to the same object.