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By Michael McIntyre

mikemc@getdotnetcode.com

This article introduces the Queue class and provides example code that demonstrates how to use a Queue object. The Queue class is located within the .NET Framework’s System.Collections namespace.

A Queue object is a first-in, first-out collection of objects. Queues are useful for storing things in the order they were received for sequential processing. Objects stored in a Queue collection are inserted at one end and removed from the other.

The following code snippets demonstrate how to use a Queue object to keep track of each player’s turn in a game application.

Example One – Declare and instantiate a Queue object.

' Declare a variable of type Queue named _PlayerQueue.

' Use a Queue constructor to create a new Queue object.

' Assign the address (reference) of the new object

' to the _PlayerQueue variable.

Private _PlayerQueue As New Queue()

Example Two – A method named FillPlayerQueue is used to fill the _PlayerQueue object with player names

Private Sub FillPlayerQueue()

   ' The Queue Enqueue method is used to add objects to the front of a Queue.

   ' Add four players to _PlayerQueue.

   _PlayerQueue.Enqueue("Mike")

   _PlayerQueue.Enqueue("Mary")

   _PlayerQueue.Enqueue("Bill")

   _PlayerQueue.Enqueue("Tony")

   ' By default a Queue is given capacity to hold 32 objects.

   ' The Queue TrimToSize method sets the capacity to the

   ' actual number of elements in the Queue.

   ' Trim the size of _PlayerQue to four players.

   _PlayerQueue.TrimToSize()

End Sub

Example Three - A function named GetNextPlayer pulls a player from the front of the _PlayerQueue and then adds same player back to the _PlayerQueue – at the end of the Queue - so the player’s turn will come up again after the other players have had their turn.

Private Function GetNextPlayer() As String

   ' Declare a variable of type String named player.

   Dim player As String

   ' The Queue Dequeue method removes and returns the object

   ' at the beginning of the Queue.

   ' Get the next player from the _PlayerQueue.

   player = _PlayerQueue.Dequeue.ToString

   ' Trim _PlayerQueue to size.

   _PlayerQueue.TrimToSize()

   ' The Queue Enqueue adds an object to the end of the Queue.

   ' Add the player back to the Queue, at the end of the Queue

   ' so the player's turn will come up again after the other

   ' players have their turns.

   _PlayerQueue.Enqueue(player)

   ' Return the player.

   Return player

End Function

Example Four - A function named ReportPlayerQueueStatus uses Queue methods to report the next player, current player order, and the number of players.

Private Function ReportPlayerQueueStatus() As String

   ' Declare a variable of type String named report.

   Dim report As String

   ' Build the report.

   report += "Player Queue Status Report" & vbCrLf

   report += "----------------------------" & vbCrLf

   ' The Queue Peek method returns the object at the front of the Queue

   ' without removing it from the Queue.

   report += "Next player will be " & _PlayerQueue.Peek.ToString & "." & vbCrLf

   ' The Queue Count method returns the number of objects in a Queue.

   report += "Number of players is " & _PlayerQueue.Count.ToString & vbCrLf & vbCrLf

   ' Add Title for player list.

   report += "Players" & vbCrLf

   report += "----------------------------"

   ' The Queue CopyTo method is used to copy the objects

   ' in a Queue to an array.

   ' Copy _PlayerQueue objects to an array.

   Dim players(_PlayerQueue.Count) As String

   _PlayerQueue.CopyTo(players, 0)

   ' List the players in the Queue.

   Dim player As String

   For Each player In players

       report += player & vbCrLf

   Next

   Return report

End Function

Learn more about the Queue class by clicking here.

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