Generic Queue and Non-generic Queue

Queue<T> and Queue are first-in first-out (FIFO) data structures, providing methods to Enqueue (add an item to the tail of the queue) and Dequeue (retrieve and remove the item at the head of the queue). A Peek method is also provided to return the element at the head of the queue without removing it, and a Count property.

The generic version of Queue has the following methods:

 
public class Queue<T> : IEnumerable<T>, ICollection, IEnumerable
{
    public Queue();
    public Queue (IEnumerable<T> collection); // Copies existing elements 
    public Queue (int capacity);  // To lessen auto-resizing 
    public void Clear();
    public bool Contains (T item);
    public void CopyTo (T[] array, int arrayIndex);
    public int Count { get; }
    public T Dequeue();
    public void Enqueue (T item);
    public Enumerator<T> GetEnumerator(); // To support foreach 
    public T Peek();
    public T[] ToArray();
    public void TrimExcess();
}

The following is an example of using Queue<int>:

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

class Sample
{
    public static void Main()
    {
        var q = new Queue<int>();
        q.Enqueue(10);
        q.Enqueue(20);
        int[] data = q.ToArray(); // Exports to an array 
        Console.WriteLine (q.Count);   
        Console.WriteLine (q.Peek()); 
        Console.WriteLine(q.Dequeue());   
        Console.WriteLine (q.Dequeue()); 
        Console.WriteLine(q.Dequeue());  

    }

}

The output:


2
10
10
20

Unhandled Exception: System.InvalidOperationException: Queue empty.
   at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resour
ce)
   at System.Collections.Generic.Queue`1.Dequeue()
   at Sample.Main() in c:\g\Program.cs:line 18
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