From: 011netservice@gmail.com
Date: 2022-04-24
Subject: CollectionGeneric-Queue.txt

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----------
2015-01-26

using System;
using System.Collections.Generic;

class Example
{
    public static void Main()
    {
        Queue<string> numbers = new Queue<string>();
        numbers.Enqueue("one");
        numbers.Enqueue("two");
        numbers.Enqueue("three");
        numbers.Enqueue("four");
        numbers.Enqueue("five");

        // A queue can be enumerated without disturbing its contents.
        foreach( string number in numbers )
        {
            Console.WriteLine(number);
        }

        Console.WriteLine("\nDequeuing '{0}'", numbers.Dequeue());
        Console.WriteLine("Peek at next item to dequeue: {0}", 
            numbers.Peek());
        Console.WriteLine("Dequeuing '{0}'", numbers.Dequeue());

        // Create a copy of the queue, using the ToArray method and the
        // constructor that accepts an IEnumerable<T>.
        Queue<string> queueCopy = new Queue<string>(numbers.ToArray());

        Console.WriteLine("\nContents of the first copy:");
        foreach( string number in queueCopy )
        {
            Console.WriteLine(number);
        }
        
        // Create an array twice the size of the queue and copy the
        // elements of the queue, starting at the middle of the 
        // array. 
        string[] array2 = new string[numbers.Count * 2];
        numbers.CopyTo(array2, numbers.Count);
        
        // Create a second queue, using the constructor that accepts an
        // IEnumerable(Of T).
        Queue<string> queueCopy2 = new Queue<string>(array2);

        Console.WriteLine("\nContents of the second copy, with duplicates and nulls:");
        foreach( string number in queueCopy2 )
        {
            Console.WriteLine(number);
        }

        Console.WriteLine("\nqueueCopy.Contains(\"four\") = {0}", 
            queueCopy.Contains("four"));

        Console.WriteLine("\nqueueCopy.Clear()");
        queueCopy.Clear();
        Console.WriteLine("\nqueueCopy.Count = {0}", queueCopy.Count);
    }
}

/* This code example produces the following output:

one
two
three
four
five

Dequeuing 'one'
Peek at next item to dequeue: two
Dequeuing 'two'

Contents of the copy:
three
four
five

Contents of the second copy, with duplicates and nulls:



three
four
five

queueCopy.Contains("four") = True

queueCopy.Clear()

queueCopy.Count = 0
 */
 
Remarks
This class implements a generic queue as a circular array. 
Objects stored in a Queue<T> are inserted at one end and removed from the other. 
Queues and stacks are useful when you need temporary storage for information; 
that is, when you might want to discard an element after retrieving its value. 
Use Queue<T> if you need to access the information in the same order that it is stored in the collection. 
Use Stack<T> if you need to access the information in reverse order. 
Use ConcurrentQueue<T> or ConcurrentStack<T> if you need to access the collection from multiple threads concurrently.

Three main operations can be performed on a Queue<T> and its elements:
1. Enqueue adds an element to the end of the Queue<T>.
2. Dequeue removes the oldest element from the start of the Queue<T>.
3. Peek peek returns the oldest element that is at the start of the Queue<T> but does not remove it from the Queue<T>.

The capacity of a Queue<T> is the number of elements the Queue<T> can hold. 
As elements are added to a Queue<T>, the capacity is automatically increased as required by reallocating the internal array. 
The capacity can be decreased by calling TrimExcess.

Queue<T> accepts null as a valid value for reference types and allows duplicate elements.