VB.Net Tutorial/Collections/Your Queue

Define your own queue based on the 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 Queue
   Inherits List
   Public Sub New()
      MyBase.New("queue")
   End Sub
   Public Sub Enqueue(ByVal dataValue As Object)
      MyBase.InsertAtBack(dataValue)
   End Sub
   Public Function Dequeue() As Object
      Return MyBase.RemoveFromFront()
   End Function
End Class

Module modQueueTest
   Sub Main()
      Dim queue As Queue = New Queue()
      queue.Enqueue(Convert.ToChar("$"))
      queue.Enqueue(123)
      queue.Enqueue("hello")
      queue.Enqueue(True)
      queue.Print()
      Dim removedObject As Object = Nothing
      Try
         While True
            removedObject = queue.Dequeue()
            Console.WriteLine(removedObject & " dequeue")
            queue.Print()
         End While
      Catch emptyListException As EmptyListException
         Console.Error.WriteLine(emptyListException.StackTrace)
      End Try
   End Sub
End Module

The queue is: $ 123 hello True
$ dequeue
The queue is: 123 hello True
123 dequeue
The queue is: hello True
hello dequeue
The queue is: True
True dequeue
Empty queue
   at List.RemoveFromFront()
   at modQueueTest.Main()