Wrapping an object with another in VB 2013 - vb.net

Question

I am trying to wrap an instance of a created class with another that share the same super class in Visual Basic 2013. I'm new to VB and been struggling with this.
This is for a Java to VB conversion..
Code example of what I have written:
' Abstract product creator Class
Public MustInherit Class PizzaMaker
' Abstract Method to create a pizza
Public MustOverride Function createPizza(ByRef size As Integer, ByRef crust As String) As Pizza
Public Function orderPizza(ByRef size, ByRef crust) As Pizza
Dim pizza As Pizza
pizza = createPizza(size, crust)
Return pizza
End Function
End Class
' Concrete factory Class
Public Class MargheritaMaker
Inherits PizzaMaker
' Override abstrat method in superclass
Public Overrides Function createPizza(ByRef size As Integer, ByRef crust As String) As Pizza
Dim pizza As New MargheritaPizza(size, crust)
Return pizza
End Function
End Class
' Abstract component product Class
Public MustInherit Class Pizza
' Consatant variables used for pizza size
Public Const SMALL As Integer = 1
Public Const MEDIUM As Int16 = 2
Public Const LARGE As Int16 = 3
Public Const EXTRA_LARGE As Int16 = 4
' Crust type of pizza
Private crustType As String
' Size of the pizza
Private size As Int16
' Description of the pizza
Public description As String = "Pizza"
' Abstract method to return the cost of the pizza
Public MustOverride Function getCost() As Double
' Returns size description
Public Function getSizeDescription() As String
Dim desc As String
' Determin pizza size and return String description
If (size = 1) Then
desc = "Small"
ElseIf (size = 2) Then
desc = "Medium"
ElseIf (size = 3) Then
desc = "Large"
Else
desc = "Extra Large"
End If
Return desc
End Function
Public Function getCrust() As String
Return crustType
End Function
' Sets the pizza crust type
Public Sub setCrust(ByRef crust)
crustType = crust
End Sub
' Returns the pizza size
Public Function getSize() As Integer
Return size
End Function
' Set the size of our Pizza
Public Sub setSize(ByVal i)
size = i
End Sub
' Returns the String description of the pizza
Public Function getDescription() As String
Return getSizeDescription() + " " + crustType + " " + description
End Function
End Class
' Concrete component product Class defining a Margherita Pizza
Public Class MargheritaPizza
Inherits Pizza
'Dim cost
' Constructor set's the Pizza size, crust type & description
Sub New(ByRef size As Integer, ByRef crust As String)
setSize(size)
setCrust(crust)
description = "Margherita Pizza"
End Sub
' Returns the Pizza base cost based on it's size
Public Overrides Function getCost() As Double
Dim cost As Double
If (getSize() = Pizza.SMALL) Then
'Console.Write("in if" & vbNewLine)
cost = 9.5
ElseIf (getSize() = Pizza.MEDIUM) Then
cost = 10.5
ElseIf (getSize() = Pizza.LARGE) Then
cost = 11.5
ElseIf (getSize() = Pizza.EXTRA_LARGE) Then
cost = 12.5
End If
'Console.Write("in if" * vbNewLine)
Return cost
End Function
End Class
' Abstract component product decorator Class
Public MustInherit Class PizzaDecorator
Inherits Pizza
' Abstract method that returns decorator description
Public MustOverride Overloads Function getDescription()
End Class
' Concrete component product decorator Class (used as Object wrapper)
Public Class Cheese
Inherits PizzaDecorator
Dim pizza ' As Pizza
' Check that the construtor paramaters are correct!!! Also check scope of variables!!!
Sub New(ByVal pizz)
pizza = pizz
'pizza.setSize(pizz.getSize())
'pizza.setCrust(pizz.getCrust())
End Sub
' Returns cost of product by delegating call to wrapped objects
Public Overrides Function getCost() As Double
Dim cost ' As Double = pizza.getCost()
If (pizza.getSize() = pizza.SMALL) Then
Console.Write(" In cheese pizza = SMALL" & vbNewLine)
cost += 0.1
ElseIf (pizza.getSize() = pizza.MEDIUM) Then
cost += 0.2
ElseIf (pizza.getSize() = pizza.LARGE) Then
cost += 0.3
ElseIf (pizza.getSize() = pizza.EXTRA_LARGE) Then
cost += 0.4
End If
Console.Write(" Pizza size = " + pizza.getSize().ToString & vbNewLine)
Console.Write(" in end if" & vbNewLine)
Return cost + pizza.getCost()
End Function
Public Overrides Function getDescription() As Object
Return pizza.getDescription() + ", Extra Cheese"
End Function
End Class
Then run a test with this:
Public Class TestForm
Public margheritaM ' As MargheritaMaker
Public pizza ' As Pizza
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
'Dim m As New MargheritaMaker()
'Dim pizza
'Dim margheritaM As New MargheritaMaker()
margheritaM = New MargheritaMaker()
pizza = margheritaM.createPizza(1, "Deep Pan")
MargheritaBox.AppendText(pizza.getDescription() & vbNewLine)
End Sub
Private Sub CheeseButton_Click(sender As Object, e As EventArgs) Handles CheeseButton.Click
'pizza As New Cheese(pizza)
pizza = New Cheese(pizza)
MargheritaBox.AppendText(pizza.getDescription() & vbNewLine)
End Sub
Private Sub CostButton_Click(sender As Object, e As EventArgs) Handles CostButton.Click
MargheritaBox.AppendText(pizza.getCost() & vbNewLine)
End Sub
Private Sub PepperoniButton_Click(sender As Object, e As EventArgs) Handles PepperoniButton.Click
pizza = New Pepperoni(pizza)
MargheritaBox.AppendText(pizza.getDescription() & vbNewLine)
End Sub
End Class
I assumed I could create a MargheritaPizza objcet with Button1 click and assign a pizza object to pizza via it's factory method createPizza
then on cheeseButton click I could wrap the pizza object created with the call pizza = New Cheese(pizza)!! The cheese class encapsulates the extra topping for the pizza. I thought that I could then call cost on the original pizza object wiich would delegate the cost through the wrapped objects?? As in the Decorator Pattern.
Some screen shot of output below:
Here I clicked create pizza then calculate cost then extra cheese finally calculate cost, all seems well!
This time I also clicked extra cheese and calculate cost, but the cost is not delegating through the objects correctly!
Here I added several extra cheese and also show some output to the console window for the test, the console window shows the size of the pizza each time the object is wrapped and shows that pizza size is 0 except on the inner most wrapper...What am I doing wrong??
My first language is Java and have no problem with this technique in the past, but new to VB 2013 and appreciate some help here..
All constructive comments welcome.
Many thanks
Please ignore code that's been commented out during testing

Answer 1

Wrapping
Firstly, and this is only my opinion, the term wrapping are used when you're dealing with NotInheritable classes.
Example:
Public Class String2
Public Sub New(s As String)
Me.s = s
End Sub
Default Public ReadOnly Property Chars(index As Integer) As Char
Get
Return Me.s.Chars(index)
End Get
End Property
Public ReadOnly Property Length() As Integer
Get
Return s.Length
End Get
End Property
Private ReadOnly s As String
End Class
Base classes
Secondly, you're overcomplicating this. The following code are stripped to make it more readable. Note that this is not a final solution.
Start by defining a Crust and a Size enum.
Public Enum PizzaCrust As Integer
[Default] = 0
DeepPan = 1
End Enum
Public Enum PizzaSize As Integer
S = 0
M = 1
L = 2
XL = 3
End Enum
You only need two base classes, Pizza and Extra.
Public MustInherit Class Pizza
Public Property Crust() As PizzaCrust
MustOverride ReadOnly Property Description() As String
Public ReadOnly Property Extras() As List(Of Extra)
MustOverride ReadOnly Property Name() As String
Public Property Size() As PizzaSize
Public Function CalculateCost() As Decimal
Dim value As Decimal = Me.GetBaseCost(Me.Size)
For Each extr As Extra In Me.Extras
value += extr.Cost
Next
Return value
End Function
Protected MustOverride Function GetBaseCost(size As PizzaSize) As Decimal
End Class
Public MustInherit Class Extra
Public MustOverride ReadOnly Property Name() As String
Public MustOverride ReadOnly Property Description() As String
Public MustOverride ReadOnly Property Cost() As Decimal
End Class
Pizzas
Create a namespace named Pizzas and put all of your pizzas here.
Namespace Pizzas
Public Class Margarita
Inherits Pizza
Public Overrides ReadOnly Property Description() As String
Public Overrides ReadOnly Property Name() As String
Protected Overrides Function GetBaseCost(size As PizzaSize) As Decimal
Select Case size
Case PizzaSize.S
Return 10
Case PizzaSize.M
Return 15
Case PizzaSize.L
Return 20
Case PizzaSize.XL
Return 30
Case Else
Return 0
End Select
End Function
End Class
Public Class Quattro
Inherits Pizza
Public Overrides ReadOnly Property Description() As String
Public Overrides ReadOnly Property Name() As String
Protected Overrides Function GetBaseCost(size As PizzaSize) As Decimal
End Class
End Namespace
Extras
Finally, create a namespace named Extras and put all of the extras here.
Namespace Extras
Public Class Cheese
Inherits Extra
Public Overrides ReadOnly Property Cost() As Decimal
Public Overrides ReadOnly Property Description() As String
Public Overrides ReadOnly Property Name() As String
End Class
Public Class Ham
Inherits Extra
Public Overrides ReadOnly Property Cost() As Decimal
Public Overrides ReadOnly Property Description() As String
Public Overrides ReadOnly Property Name() As String
End Class
Public Class Pineapple
Inherits Extra
Public Overrides ReadOnly Property Cost() As Decimal
Public Overrides ReadOnly Property Description() As String
Public Overrides ReadOnly Property Name() As String
End Class
End Namespace
Usage
Now, to create a new Margarita pizza, one would do it like this:
Dim pizza As New Pizzas.Margarita()
pizza.Size = PizzaSize.L
pizza.Crust = PizzaCrust.DeepPan
pizza.Extras.Add(New Extras.Ham())
pizza.Extras.Add(New Extras.Cheese())