Programming Visual Basic 2005

Copy Constructors

A copy constructor creates a new object by copying variables from an existing object of the same type. For example, you might want to pass a Time object to a Time constructor so that the new Time object has the same values as the old one.

Visual Basic 2005 does not provide a copy constructor, so if you want one you must provide it yourself. Such a constructor copies the elements from the original object into the new one, as shown in Example 18-4.

Example 18-4. Copy constructor

Public Sub New(ByVal existingObject As Time)
   year = existingObject.year
   month = existingObject.month
   dayOfMonth = existingObject.dayOfMonth
   hour = existingObject.hour
   minute = existingObject.minute
   second = existingObject.second
End Sub

A copy constructor is invoked by instantiating an object of type Time and passing it the name of the Time object to be copied:

Dim t2 As New Time(timeObject)

The Me Keyword

The keyword Me refers to the current instance of an object. The Me reference is a hidden reference to every non-Shared method of a class (Shared methods are discussed later). Each method can refer to the other methods and variables of that object by way of the Me reference.

The Me reference may be used to distinguish instance members that have the same name as parameters, as in the following:

Public Sub SomeMethod(ByVal hour As Integer)
   Me.hour = hour
End Sub

In this example, SomeMethod takes a parameter (hour) with the same name as a member variable of the class. The Me reference is used to resolve ...