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Introduction to Collections - Queues

Introduction to Collections - Queues, Introducing the Queue class

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SixOfEleven
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13 Apr, 2009 - 09:24 AM

Post #1

Introduction to Queues.

Queues are an interesting collection. Queues represent a first-in-first-out(FIFO) collection. Think of a queue like a line at a grocery store. Customers come to the check out and are processed in the order that they came in. If you needed to program that sort of situation you could use a queue.

Queues are used a lot in real life simulations. For example, you need to model how a bank processes customers to find out the best number of tellers to have at the windows at a given time. You would create a simulation that would process how many customers come into the bank, the average wait time of a custmoer. How many customers each teller processes.

You could also use a queue in a client-server application. As each request comes into the server it is put into a queue to be processed. The server would process the requests in the order that they came in.

This is how you would create a queue:

CODE

Queue<class> myQueue = new Queue<class>();

When you need to add an object to the queue you use the Enqueue method like this:

CODE

myQueue.Enqueue(object);

To get the first object in the queue you use the Dequeue method.

CODE

objectVariable = myQueue.Dequeue();

Sometimes you may want to see what the first object in the queue is without removing it from the queue. You would do this using the Peek method like this:

CODE

object = myQueue.Peek();

To determine how many objects are in a queue you would use the Count property like this:

CODE

intNumber = myQueue.Count;

If you need to empty the queue you would use the Clear method like this:

CODE

myQueue.Clear();

If you need to see the objects in your queue there two easy ways to do it. You can use a simple for loop or a foreach loop. This is how to do each one in turn:

CODE

for (int i = 0; i < myQueue.Count; i++)
{
Console.WriteLine(myQueue[i].ToString());
}

CODE

foreach (class o in myQueue)
{
Console.WriteLine(o.ToString());
}

This is a simple program that demonstrates the use of queues:

CODE

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace QueuesDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            Queue<string> myQueue = new Queue<string>();

            myQueue.Enqueue("Bobby");
            myQueue.Enqueue("Margaret");
            myQueue.Enqueue("Timmy");
            myQueue.Enqueue("Wendy");
            myQueue.Enqueue("Linda");

            WriteQueue(myQueue);

            Console.ReadLine();

            while (myQueue.Count > 0)
            {
                string name;

                name = myQueue.Peek();

                Console.WriteLine("Removing {0} form the queue\n\r", name);

                myQueue.Dequeue();

                WriteQueue(myQueue);
                Console.ReadLine();
            }

        }

        private static void WriteQueue(Queue<string> myQueue)
        {

            Console.WriteLine("This is the queue:");

            if (myQueue.Count == 0)
                Console.WriteLine("The queue is empty.");

            foreach (string o in myQueue)
                Console.WriteLine(o);
        }

    }
}