Queue(Of T).Clear Method ()


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Removes all objects from the Queue(Of T).

Namespace:   System.Collections.Generic
Assembly:  System (in System.dll)

Public Sub Clear

Count is set to zero, and references to other objects from elements of the collection are also released.

The capacity remains unchanged. To reset the capacity of the Queue(Of T), call TrimExcess. Trimming an empty Queue(Of T) sets the capacity of the Queue(Of T) to the default capacity.

This method is an O(n) operation, where n is Count.

The following code example demonstrates several methods of the Queue(Of T) generic class, including the Clear method.

The code example creates a queue of strings with default capacity and uses the Enqueue method to queue five strings. The elements of the queue are enumerated, which does not change the state of the queue. The Dequeue method is used to dequeue the first string. The Peek method is used to look at the next item in the queue, and then the Dequeue method is used to dequeue it.

The ToArray method is used to create an array and copy the queue elements to it, then the array is passed to the Queue(Of T) constructor that takes IEnumerable(Of T), creating a copy of the queue. The elements of the copy are displayed.

An array twice the size of the queue is created, and the CopyTo method is used to copy the array elements beginning at the middle of the array. The Queue(Of T) constructor is used again to create a second copy of the queue containing three null elements at the beginning.

The Contains method is used to show that the string "four" is in the first copy of the queue, after which the Clear method clears the copy and the Count property shows that the queue is empty.

Imports System
Imports System.Collections.Generic

Module Example

    Sub Main

        Dim numbers As New Queue(Of String)

        ' A queue can be enumerated without disturbing its contents.
        For Each number As String In numbers

        Console.WriteLine(vbLf & "Dequeuing '{0}'", numbers.Dequeue())
        Console.WriteLine("Peek at next item to dequeue: {0}", _
        Console.WriteLine("Dequeuing '{0}'", numbers.Dequeue())

        ' 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())

        Console.WriteLine(vbLf & "Contents of the first copy:")
        For Each number As String In queueCopy

        ' 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)

        Console.WriteLine(vbLf & _
            "Contents of the second copy, with duplicates and nulls:")
        For Each number As String In queueCopy2

        Console.WriteLine(vbLf & "queueCopy.Contains(""four"") = {0}", _

        Console.WriteLine(vbLf & "queueCopy.Clear()")
        Console.WriteLine(vbLf & "queueCopy.Count = {0}", _
    End Sub
End Module

' This code example produces the following output:
'Dequeuing 'one'
'Peek at next item to dequeue: two
'Dequeuing 'two'
'Contents of the copy:
'Contents of the second copy, with duplicates and nulls:
'queueCopy.Contains("four") = True
'queueCopy.Count = 0

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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