collections.Queue with a definite capacity where old objects expire


This is in VB.Net although C# may be acceptable too if it can be translated.

I'd like to use something FIFO like System.Collections.Generic.Queue but I'd also like it to have a maximum capacity so that if there are too many items in the queue, the oldest items will fall out of the queue (or expire) as new items are added. I don't want this queue to grow indefinitely.

Is there any way to do this, or is there another object like Queue that has this functionality?

In case you're still confused, this is what I need..

Queue (with a maximum capacity of 3):

This Queue (though I'm not sure if it can be done) should have a maximum size of 3.

When I add in A,B,C, in that order, A will be in 0, B will be in 1, and C will be in 2, like this:

0) A
1) B
2) C

But if I add a fourth item D, A will expire, B will be in 0, C will be in 1, and D will be in 2, like this:

0) B
1) C
2) D

I also need to pull items off the stack in a FIFO manner (like Queue's .dequeue), like this (from the B,C,D queue):

Dequeue (pop B off the stack), Dequeue (pop C off the stack) then the stack will look like this:

0) D

Thanks in advance!

Who is Participating?
Fernando SotoRetiredCommented:
Hi jakeryan;

Here is a Queue Collections Class modified to do what you want.

Public Class SmallQueue1
    Inherits System.Collections.Queue

    Public Sub New()
    End Sub

    Public Sub New(ByVal col As ICollection)
    End Sub

    Public Sub New(ByVal capacity As Integer)
        ' As you only want a queue of three set the queue to be three
        ' Do not need to set the grow factor
    End Sub

    Public Sub New(ByVal capacity As Integer, ByVal growFactor As Single)
        ' As you only want a queue of three set the queue to be three
    End Sub

    Public Overrides Sub Enqueue(ByVal obj As Object)

        If Me.Count > 2 Then
        End If

    End Sub

End Class

Now in the Form you can do this.

        Dim myQueue As New SmallQueue1

        Console.WriteLine(myQueue.Dequeue())    ' Prints out E
        Console.WriteLine(myQueue.Dequeue())    ' Prints out F
        Console.WriteLine(myQueue.Dequeue())    ' Prints out G

You can modify the SmallQueue1 Calss as needed.

Carl TawnSystems and Integration DeveloperCommented:
I'm pretty sure you'll have to either subclass or wrap the Queue class and implement the required functionality yourself.

Maybe you'd be better of with a simple array.
Mike TomlinsonMiddle School Assistant TeacherCommented:
It would be easy enough to wrap an ArrayList in a Class to give you this functionality...
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jakeryanAuthor Commented:

Based on the example you've given, that looks like it would do exactly what I need! Unfortunately, due to a more pressing bug I've had to roll back my project to a few weeks ago. I can't wait to try it out though. I just wanted to give you a heads up I didn't abandon this.

Fernando SotoRetiredCommented:
No problem. Let me know if you need any other help with this.

Fernando SotoRetiredCommented:
Hi Bob;

I would like to see a resolution to the problem seeming I gave jakeryan a solution that works and his statement was, "Based on the example you've given, that looks like it would do exactly what I need!"."


jakeryanAuthor Commented:
Not abandoned, I needed more time. Thank you FernandoSoto! I'm sorry I couldn't test this earlier, but due to a very nasty bug in my program popping up, I had to resort to an older version and work my way back up to present. Your queue class worked for me!
Fernando SotoRetiredCommented:
No problem. Glad I was able to help. ;=)
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