VB.Net Tutorial/Collections/Your Stack

Define your own Stack class based on List

Public Class List
   Private firstNode As Node
   Private lastNode As Node
   Private name As String
   Public Sub New(ByVal listName As String)
      name = listName
      firstNode = Nothing
      lastNode = Nothing
   End Sub
   Public Sub New()
      MyClass.New("list")
   End Sub " New
   Public Sub InsertAtFront(ByVal insertItem As Object)
      SyncLock (Me) 
         If IsEmpty() Then
            lastNode = New Node(insertItem)
            firstNode = lastNode
         Else 
            firstNode = New Node(insertItem, firstNode)
         End If
      End SyncLock
   End Sub
   Public Sub InsertAtBack(ByVal insertItem As Object)
      SyncLock (Me)
         If IsEmpty() Then
            lastNode = New Node(insertItem)
            firstNode = lastNode
         Else
            lastNode.NextNode = New Node(insertItem)
            lastNode = lastNode.NextNode
         End If
      End SyncLock
   End Sub
   Public Function RemoveFromFront() As Object
      SyncLock (Me)
         Dim removeItem As Object = Nothing
         If IsEmpty() Then
            Throw New EmptyListException(name)
         End If
         removeItem = firstNode.Data
         If firstNode Is lastNode Then
            firstNode = Nothing
            lastNode = Nothing
         Else
            firstNode = firstNode.NextNode
         End If
         Return removeItem 
      End SyncLock
   End Function
   Public Function RemoveFromBack() As Object
      SyncLock (Me)
         Dim removeItem As Object = Nothing
         If IsEmpty() Then
            Throw New EmptyListException(name)
         End If
         removeItem = lastNode.Data
         If firstNode Is lastNode Then
            lastNode = Nothing
            firstNode = lastNode
         Else
            Dim current As Node = firstNode
            While (Not (current.NextNode Is lastNode))
               current = current.NextNode
            End While
            lastNode = current
            current.NextNode = Nothing
         End If
         Return removeItem
      End SyncLock
   End Function
   
   Public Function IsEmpty() As Boolean
      SyncLock (Me)
         If firstNode Is Nothing Then
            Return True
         Else
            Return False
         End If
      End SyncLock
   End Function
   
   Public Overridable Sub Print()
      SyncLock (Me)
         If IsEmpty() Then
            Console.WriteLine("Empty " & name)
            Return
         End If
         Console.Write("The " & name & " is: ")
         Dim current As Node = firstNode
         While Not current Is Nothing
            Console.Write(current.Data & " ")
            current = current.NextNode
         End While
         Console.WriteLine(vbCrLf)
      End SyncLock
   End Sub
End Class 
Public Class Node
   Private mData As Object
   Private mNextNode As Node
   Public Sub New(ByVal dataValue As Object)
      MyClass.New(dataValue, Nothing)
   End Sub
   Public Sub New(ByVal dataValue As Object, ByVal nextNodeValue As Object)
      mData = dataValue
      mNextNode = nextNodeValue
   End Sub
   
   Public ReadOnly Property Data() As Object
      Get
         Return mData
      End Get
   End Property
   Public Property NextNode() As Node
      Get
         Return mNextNode
      End Get
      Set(ByVal value As Node)
         mNextNode = value
      End Set
   End Property
End Class 
Public Class EmptyListException
   Inherits ApplicationException
   Public Sub New(ByVal name As String)
      MyBase.New("The " & name & " is empty")
   End Sub " New
End Class

Public Class Stack
   Inherits List
   Public Sub New()
      MyBase.New("stack")
   End Sub " New
   Public Sub Push(ByVal dataValue As Object)
      MyBase.InsertAtFront(dataValue)
   End Sub 
   Public Function Pop() As Object
      Return MyBase.RemoveFromFront()
   End Function 
End Class
Module modStackInheritanceTest
   Sub Main()
      Dim stack As Stack = New Stack()
      stack.Push(True) " add Boolean
      stack.Push(Convert.ToChar("$")) " add Char
      stack.Push(123)
      stack.Push("aString") " add String
      stack.Print()
      Dim removedObject As Object = Nothing
      Try
         While True
            removedObject = stack.Pop()
            Console.WriteLine(removedObject & " popped")
            stack.Print()
         End While
      Catch emptyListException As EmptyListException
         Console.Error.WriteLine(emptyListException.StackTrace)
      End Try
   End Sub 
End Module

The stack is: aString 123 $ True
aString popped
The stack is: 123 $ True
123 popped
The stack is: $ True
$ popped
The stack is: True
True popped
Empty stack
   at List.RemoveFromFront()
   at modStackInheritanceTest.Main()