Section 8.5. Copy Constructors

8.5 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 which will create a new Time object ( ), as shown in Example 8-7.

Example 8-7. 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( )         System.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 theHour As Integer, _    ByVal theMinute As Integer)       Year = theYear       Month = theMonth       Date = theDate       Hour = theHour       Minute = theMinute       Second = theSecond    End Sub    Public Sub New(existingObject As Time)       Year = existingObject.Year       Month = existingObject.Month       Date = existingObject.Date       Hour = existingObject.Hour       Minute = existingObject.Minute       Second = existingObject.Second    End Sub End Class 'Time Module Module1    Sub Main( )       Dim timeObject As New Time(2005, 3, 25, 9, 35)       Dim t2 As New Time(timeObject)       timeObject.DisplayCurrentTime( )       t2.DisplayCurrentTime( )    End Sub End Module 

  Output:  3/25/2005 9:35:30 3/25/2005 9:35:30