Programming Visual Basic .NET, Second Edition

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.

VB.NET 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:

Public Sub New(ByVal existingObject As Time)
   year = existingObject.Year
   month = existingObject.Month
   date = existingObject.Date
   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(existingObject)

Here an existing Time object (existingObject) is passed as a parameter to the copy constructor that will create a new Time object ( ), as shown in Example 5-7.

Example 5-7. Copy constructor

Option Strict On Imports System Public Class Time ' Private variables Private year As Integer Private month As Integer Private date As Integer Private hour As Integer Private minute As Integer Private second As Integer = 30 ' Public methods Public Sub DisplayCurrentTime( ) Console.WriteLine("{0}/{1}/{2} {3}:{4}:{5}", _ month, date, year, hour, minute, second) End Sub 'DisplayCurrentTime Public Sub New( _ ByVal theYear As Integer, _ ByVal theMonth As Integer, _ ByVal theDate As Integer, _ ByVal ...