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question about sub New() in a classI found this code here below (about cartitems and shoppingcart) and I have two questions about sub New(). In the first class CartItem, there is two times sub New(): Public Sub New() End Sub and Public Sub New(ByVal ProductID As Integer, ByVal ProductName As String, ...) _productID = ProductID _productName = ProductName ... End Sub In the second class WroxShoppingCart, there is one time sub New(): Public Sub New() _items = New List(Of CartItem) _dateCreated = DateTime.Now End Sub My questions are: 1) why an empty sub New() in class CartItem 2) why are there parameters defined in sub New() of class CartItem and not in sub New() of class WroxShoppingCart? Thanks Bob Part of code: (hopely this is enough) --------------- Public Class CartItem Private _productID As Integer Private _productName As String ... Public Sub New() End Sub Public Sub New(ByVal ProductID As Integer, ByVal ProductName As String, ...) _productID = ProductID _productName = ProductName ... End Sub Public Property ProductID() As Integer Get Return _productID End Get Set(ByVal value As Integer) _productID = value End Set End Property .... End Class Public Class WroxShoppingCart Private _dateCreated As DateTime Private _lastUpdate As DateTime Private _items As List(Of CartItem) Public Sub New() _items = New List(Of CartItem) _dateCreated = DateTime.Now End Sub End Class Bob wrote:
Show quoteHide quote > Hi, If you did not include the default constructor you would no longer be> > I found this code here below (about cartitems and shoppingcart) and I have > two questions about sub New(). > > In the first class CartItem, there is two times sub New(): > Public Sub New() > End Sub > > and > > Public Sub New(ByVal ProductID As Integer, ByVal ProductName As String, ...) > _productID = ProductID > _productName = ProductName > ... > End Sub > > > In the second class WroxShoppingCart, there is one time sub New(): > Public Sub New() > _items = New List(Of CartItem) > _dateCreated = DateTime.Now > End Sub > > My questions are: > 1) why an empty sub New() in class CartItem able to create objects of type cartitem without passing parameters. In other words: Dim c As CartItem = New CartItem() would no longer be valid. The compiler will only provide a default constructor as long as you don't add your own. As soon as you add a constructor to your class, then it's up to you to provide the default. > 2) why are there parameters defined in sub New() of class CartItem and not Because they are not needed in WroxShoppingCart... That may not sound> in sub New() of class WroxShoppingCart? > like much of an answer, but it is true. WroxShoppingCart is simply a container for CartItem's. It provides methods to manipulate and store cartitems. But, it doesn't need to know details of the individual cartitems - it just needs to know that they are cartitems. -- Tom Shelton Bob,
I tell it in another way than Tom, he is assuming something more than you maybe know. The "Sub New" is the Constructor in VB.Net. Every Class that has to be instanced (that is a class that has no Shared Members) needs a constructor. If you build a Form, than that is standard there and it is a good habbit to leave a standard constructor in every class: Public Sub New() as it is done in your sample. However sometimes you want to give the class some information at startup, that you can overload that constructer Public Sub New(Byval one as integer, byval two as integer). The compiler will see what the method looks like and takes the one that fits the best (or shows an error as there is no fitted). For the rest I leave it to the answer from Tom, because I would not write it in another way. Cor .. Show quoteHide quote "Bob" <.> schreef in bericht news:%23c1F9fDLHHA.2236@TK2MSFTNGP02.phx.gbl... > Hi, > > I found this code here below (about cartitems and shoppingcart) and I have > two questions about sub New(). > > In the first class CartItem, there is two times sub New(): > Public Sub New() > End Sub > > and > > Public Sub New(ByVal ProductID As Integer, ByVal ProductName As String, > ...) > _productID = ProductID > _productName = ProductName > ... > End Sub > > > In the second class WroxShoppingCart, there is one time sub New(): > Public Sub New() > _items = New List(Of CartItem) > _dateCreated = DateTime.Now > End Sub > > My questions are: > 1) why an empty sub New() in class CartItem > 2) why are there parameters defined in sub New() of class CartItem and not > in sub New() of class WroxShoppingCart? > > Thanks > Bob > > Part of code: (hopely this is enough) > --------------- > Public Class CartItem > Private _productID As Integer > Private _productName As String > ... > > Public Sub New() > End Sub > > Public Sub New(ByVal ProductID As Integer, ByVal ProductName As > String, ...) > _productID = ProductID > _productName = ProductName > ... > End Sub > > Public Property ProductID() As Integer > Get > Return _productID > End Get > Set(ByVal value As Integer) > _productID = value > End Set > End Property > .... > End Class > > > Public Class WroxShoppingCart > > Private _dateCreated As DateTime > Private _lastUpdate As DateTime > Private _items As List(Of CartItem) > > Public Sub New() > _items = New List(Of CartItem) > _dateCreated = DateTime.Now > End Sub > End Class > > > Bob... I think Cor explained it well in his reply. I will add that you
would do well to read a book about OOP in general. It is also my recommendation that you select a language agnostic book. There is nothing wrong with reading about VB.Net but it is important to recognize that object-orientation transcends any particular language and overloading (and constructor overloading in this case) is something almost every OOP language supports. Software development isn't about a particular set of keywords, it's the concepts that matter most. Show quoteHide quote "Bob" <.> wrote in message news:%23c1F9fDLHHA.2236@TK2MSFTNGP02.phx.gbl... > Hi, > > I found this code here below (about cartitems and shoppingcart) and I have > two questions about sub New(). > > In the first class CartItem, there is two times sub New(): > Public Sub New() > End Sub > > and > > Public Sub New(ByVal ProductID As Integer, ByVal ProductName As String, > ...) > _productID = ProductID > _productName = ProductName > ... > End Sub > > > In the second class WroxShoppingCart, there is one time sub New(): > Public Sub New() > _items = New List(Of CartItem) > _dateCreated = DateTime.Now > End Sub > > My questions are: > 1) why an empty sub New() in class CartItem > 2) why are there parameters defined in sub New() of class CartItem and not > in sub New() of class WroxShoppingCart? > > Thanks > Bob > > Part of code: (hopely this is enough) > --------------- > Public Class CartItem > Private _productID As Integer > Private _productName As String > ... > > Public Sub New() > End Sub > > Public Sub New(ByVal ProductID As Integer, ByVal ProductName As > String, ...) > _productID = ProductID > _productName = ProductName > ... > End Sub > > Public Property ProductID() As Integer > Get > Return _productID > End Get > Set(ByVal value As Integer) > _productID = value > End Set > End Property > .... > End Class > > > Public Class WroxShoppingCart > > Private _dateCreated As DateTime > Private _lastUpdate As DateTime > Private _items As List(Of CartItem) > > Public Sub New() > _items = New List(Of CartItem) > _dateCreated = DateTime.Now > End Sub > End Class > > > Ok, thanks to both of you.
Happy newyear Show quoteHide quote "Tom Leylan" <tleylan@nospam.net> schreef in bericht news:ODulTIELHHA.2236@TK2MSFTNGP02.phx.gbl... > Bob... I think Cor explained it well in his reply. I will add that you > would do well to read a book about OOP in general. It is also my > recommendation that you select a language agnostic book. There is nothing > wrong with reading about VB.Net but it is important to recognize that > object-orientation transcends any particular language and overloading (and > constructor overloading in this case) is something almost every OOP > language supports. > > Software development isn't about a particular set of keywords, it's the > concepts that matter most. > > > "Bob" <.> wrote in message news:%23c1F9fDLHHA.2236@TK2MSFTNGP02.phx.gbl... >> Hi, >> >> I found this code here below (about cartitems and shoppingcart) and I >> have two questions about sub New(). >> >> In the first class CartItem, there is two times sub New(): >> Public Sub New() >> End Sub >> >> and >> >> Public Sub New(ByVal ProductID As Integer, ByVal ProductName As String, >> ...) >> _productID = ProductID >> _productName = ProductName >> ... >> End Sub >> >> >> In the second class WroxShoppingCart, there is one time sub New(): >> Public Sub New() >> _items = New List(Of CartItem) >> _dateCreated = DateTime.Now >> End Sub >> >> My questions are: >> 1) why an empty sub New() in class CartItem >> 2) why are there parameters defined in sub New() of class CartItem and >> not in sub New() of class WroxShoppingCart? >> >> Thanks >> Bob >> >> Part of code: (hopely this is enough) >> --------------- >> Public Class CartItem >> Private _productID As Integer >> Private _productName As String >> ... >> >> Public Sub New() >> End Sub >> >> Public Sub New(ByVal ProductID As Integer, ByVal ProductName As >> String, ...) >> _productID = ProductID >> _productName = ProductName >> ... >> End Sub >> >> Public Property ProductID() As Integer >> Get >> Return _productID >> End Get >> Set(ByVal value As Integer) >> _productID = value >> End Set >> End Property >> .... >> End Class >> >> >> Public Class WroxShoppingCart >> >> Private _dateCreated As DateTime >> Private _lastUpdate As DateTime >> Private _items As List(Of CartItem) >> >> Public Sub New() >> _items = New List(Of CartItem) >> _dateCreated = DateTime.Now >> End Sub >> End Class >> >> >> > > Three,
Show quoteHide quote :-) "Bob" <.> schreef in bericht news:%237y2WUELHHA.4376@TK2MSFTNGP03.phx.gbl... > Ok, thanks to both of you. > Happy newyear > > > "Tom Leylan" <tleylan@nospam.net> schreef in bericht > news:ODulTIELHHA.2236@TK2MSFTNGP02.phx.gbl... >> Bob... I think Cor explained it well in his reply. I will add that you >> would do well to read a book about OOP in general. It is also my >> recommendation that you select a language agnostic book. There is >> nothing wrong with reading about VB.Net but it is important to recognize >> that object-orientation transcends any particular language and >> overloading (and constructor overloading in this case) is something >> almost every OOP language supports. >> >> Software development isn't about a particular set of keywords, it's the >> concepts that matter most. >> >> >> "Bob" <.> wrote in message >> news:%23c1F9fDLHHA.2236@TK2MSFTNGP02.phx.gbl... >>> Hi, >>> >>> I found this code here below (about cartitems and shoppingcart) and I >>> have two questions about sub New(). >>> >>> In the first class CartItem, there is two times sub New(): >>> Public Sub New() >>> End Sub >>> >>> and >>> >>> Public Sub New(ByVal ProductID As Integer, ByVal ProductName As String, >>> ...) >>> _productID = ProductID >>> _productName = ProductName >>> ... >>> End Sub >>> >>> >>> In the second class WroxShoppingCart, there is one time sub New(): >>> Public Sub New() >>> _items = New List(Of CartItem) >>> _dateCreated = DateTime.Now >>> End Sub >>> >>> My questions are: >>> 1) why an empty sub New() in class CartItem >>> 2) why are there parameters defined in sub New() of class CartItem and >>> not in sub New() of class WroxShoppingCart? >>> >>> Thanks >>> Bob >>> >>> Part of code: (hopely this is enough) >>> --------------- >>> Public Class CartItem >>> Private _productID As Integer >>> Private _productName As String >>> ... >>> >>> Public Sub New() >>> End Sub >>> >>> Public Sub New(ByVal ProductID As Integer, ByVal ProductName As >>> String, ...) >>> _productID = ProductID >>> _productName = ProductName >>> ... >>> End Sub >>> >>> Public Property ProductID() As Integer >>> Get >>> Return _productID >>> End Get >>> Set(ByVal value As Integer) >>> _productID = value >>> End Set >>> End Property >>> .... >>> End Class >>> >>> >>> Public Class WroxShoppingCart >>> >>> Private _dateCreated As DateTime >>> Private _lastUpdate As DateTime >>> Private _items As List(Of CartItem) >>> >>> Public Sub New() >>> _items = New List(Of CartItem) >>> _dateCreated = DateTime.Now >>> End Sub >>> End Class >>> >>> >>> >> >> > > sorry ... three
Show quoteHide quote "Cor Ligthert [MVP]" <notmyfirstn***@planet.nl> schreef in bericht news:OtRMe$ELHHA.780@TK2MSFTNGP03.phx.gbl... > Three, > > :-) > > > "Bob" <.> schreef in bericht > news:%237y2WUELHHA.4376@TK2MSFTNGP03.phx.gbl... >> Ok, thanks to both of you. >> Happy newyear >> >> >> "Tom Leylan" <tleylan@nospam.net> schreef in bericht >> news:ODulTIELHHA.2236@TK2MSFTNGP02.phx.gbl... >>> Bob... I think Cor explained it well in his reply. I will add that you >>> would do well to read a book about OOP in general. It is also my >>> recommendation that you select a language agnostic book. There is >>> nothing wrong with reading about VB.Net but it is important to recognize >>> that object-orientation transcends any particular language and >>> overloading (and constructor overloading in this case) is something >>> almost every OOP language supports. >>> >>> Software development isn't about a particular set of keywords, it's the >>> concepts that matter most. >>> >>> >>> "Bob" <.> wrote in message >>> news:%23c1F9fDLHHA.2236@TK2MSFTNGP02.phx.gbl... >>>> Hi, >>>> >>>> I found this code here below (about cartitems and shoppingcart) and I >>>> have two questions about sub New(). >>>> >>>> In the first class CartItem, there is two times sub New(): >>>> Public Sub New() >>>> End Sub >>>> >>>> and >>>> >>>> Public Sub New(ByVal ProductID As Integer, ByVal ProductName As String, >>>> ...) >>>> _productID = ProductID >>>> _productName = ProductName >>>> ... >>>> End Sub >>>> >>>> >>>> In the second class WroxShoppingCart, there is one time sub New(): >>>> Public Sub New() >>>> _items = New List(Of CartItem) >>>> _dateCreated = DateTime.Now >>>> End Sub >>>> >>>> My questions are: >>>> 1) why an empty sub New() in class CartItem >>>> 2) why are there parameters defined in sub New() of class CartItem and >>>> not in sub New() of class WroxShoppingCart? >>>> >>>> Thanks >>>> Bob >>>> >>>> Part of code: (hopely this is enough) >>>> --------------- >>>> Public Class CartItem >>>> Private _productID As Integer >>>> Private _productName As String >>>> ... >>>> >>>> Public Sub New() >>>> End Sub >>>> >>>> Public Sub New(ByVal ProductID As Integer, ByVal ProductName As >>>> String, ...) >>>> _productID = ProductID >>>> _productName = ProductName >>>> ... >>>> End Sub >>>> >>>> Public Property ProductID() As Integer >>>> Get >>>> Return _productID >>>> End Get >>>> Set(ByVal value As Integer) >>>> _productID = value >>>> End Set >>>> End Property >>>> .... >>>> End Class >>>> >>>> >>>> Public Class WroxShoppingCart >>>> >>>> Private _dateCreated As DateTime >>>> Private _lastUpdate As DateTime >>>> Private _items As List(Of CartItem) >>>> >>>> Public Sub New() >>>> _items = New List(Of CartItem) >>>> _dateCreated = DateTime.Now >>>> End Sub >>>> End Class >>>> >>>> >>>> >>> >>> >> >> > > 
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