Queue<T> Class

Type Parameters

• T
  Specifies the type of elements in the queue.

Imports System.Collections.Generic

Module Example

   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      Dim numbers As New Queue(Of 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.
      For Each number As String In numbers
         outputBlock.Text &= number & vbCrLf
      Next

      outputBlock.Text &= String.Format(vbLf & "Dequeuing '{0}'", numbers.Dequeue()) & vbCrLf
      outputBlock.Text &= String.Format("Peek at next item to dequeue: {0}", _
          numbers.Peek()) & vbCrLf
      outputBlock.Text &= String.Format("Dequeuing '{0}'", numbers.Dequeue()) & vbCrLf

      ' Create a copy of the queue, using the ToArray method and the
      ' constructor that accepts an IEnumerable(Of T).
      Dim queueCopy As New Queue(Of String)(numbers.ToArray())

      outputBlock.Text &= vbLf & "Contents of the first copy:" & vbCrLf
      For Each number As String In queueCopy
         outputBlock.Text &= number & vbCrLf
      Next

      ' Create an array twice the size of the queue, compensating
      ' for the fact that Visual Basic allocates an extra array 
      ' element. Copy the elements of the queue, starting at the
      ' middle of the array. 
      Dim array2((numbers.Count * 2) - 1) As String
      numbers.CopyTo(array2, numbers.Count)

      ' Create a second queue, using the constructor that accepts an
      ' IEnumerable(Of T).
      Dim queueCopy2 As New Queue(Of String)(array2)

      outputBlock.Text &= String.Format(vbLf & _
          "Contents of the second copy, with duplicates and nulls:") & vbCrLf
      For Each number As String In queueCopy2
         outputBlock.Text &= number & vbCrLf
      Next

      outputBlock.Text &= vbLf & String.Format("queueCopy.Contains(""four"") = {0}", _
          queueCopy.Contains("four"))

      outputBlock.Text &= vbLf & "queueCopy.Clear()" & vbCrLf
      queueCopy.Clear()
      outputBlock.Text &= String.Format(vbLf & "queueCopy.Count = {0}", _
          queueCopy.Count) & vbCrLf
   End Sub
End Module

' 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

using System;
using System.Collections.Generic;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      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)
      {
         outputBlock.Text += number + "\n";
      }

      outputBlock.Text += String.Format("\nDequeuing '{0}'", numbers.Dequeue()) + "\n";
      outputBlock.Text += String.Format("Peek at next item to dequeue: {0}",
          numbers.Peek()) + "\n";
      outputBlock.Text += String.Format("Dequeuing '{0}'", numbers.Dequeue()) + "\n";

      // 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());

      outputBlock.Text += "\nContents of the first copy:" + "\n";
      foreach (string number in queueCopy)
      {
         outputBlock.Text += number + "\n";
      }

      // 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);

      outputBlock.Text += String.Format("\nContents of the second copy, with duplicates and nulls:") + "\n";
      foreach (string number in queueCopy2)
      {
         outputBlock.Text += number + "\n";
      }

      outputBlock.Text += String.Format("\nqueueCopy.Contains(\"four\") = {0}",
          queueCopy.Contains("four")) + "\n";

      outputBlock.Text += "\nqueueCopy.Clear()" + "\n";
      queueCopy.Clear();
      outputBlock.Text += String.Format("\nqueueCopy.Count = {0}", queueCopy.Count) + "\n";
   }
}

/* 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
 */