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Array.Sort Generic Method (T[], Generic IComparer)

Note: This method is new in the .NET Framework version 2.0.

Sorts the elements in an Array using the specified IComparer generic interface.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Public Shared Sub Sort(Of T) ( _
	array As T(), _
	comparer As IComparer(Of T) _
Dim array As T()
Dim comparer As IComparer(Of T)

Array.Sort(array, comparer)
J# supports the use of generic types and methods, but not the declaration of new ones.
JScript does not support generic types and methods.

Type Parameters


The type of the elements of the array.



The one-dimensional, zero-base Array to sort


The IComparer generic interface implementation to use when comparing elements, or a null reference (Nothing in Visual Basic) to use the IComparable generic interface implementation of each element.

Exception typeCondition


array is a null reference (Nothing in Visual Basic).


comparer is a null reference (Nothing in Visual Basic), and one or more elements in array do not implement the IComparable generic interface.


The implementation of comparer caused an error during the sort. For example, comparer might not return 0 when comparing an item with itself.

If comparer is a null reference (Nothing in Visual Basic), each element of array must implement the IComparable generic interface to be capable of comparisons with every other element in array.

If the sort is not successfully completed, the results are undefined.

This method uses the QuickSort algorithm. This implementation performs an unstable sort; that is, if two elements are equal, their order might not be preserved. In contrast, a stable sort preserves the order of elements that are equal.

On average, this method is an O(n log n) operation, where n is the Length of array; in the worst case it is an O(n ^ 2) operation.

The following code example demonstrates the Sort(J[],Generic IComparer) generic method overload and the BinarySearch(J[],J,Generic IComparer) generic method overload.

The code example defines an alternative comparer for strings, named ReverseCompare, which implements the IComparer<string> (IComparer(Of String) in Visual Basic, IComparer<String^> in Visual C++) generic interface. The comparer calls the CompareTo(String) method, reversing the order of the comparands so that the strings sort high-to-low instead of low-to-high.

The array is displayed, sorted, and displayed again. Arrays must be sorted in order to use the BinarySearch method.


The calls to the Sort(J[],Generic IComparer) and BinarySearch(J[],J,Generic IComparer) generic methods do not look any different from calls to their nongeneric counterparts, because Visual Basic, C#, and C++ infer the type of the generic type parameter from the type of the first argument. If you use the MSIL Disassembler (Ildasm.exe) to examine the Microsoft intermediate language (MSIL), you can see that the generic methods are being called.

The BinarySearch(J[],J,Generic IComparer) generic method overload is then used to search for two strings, one that is not in the array and one that is. The array and the return value of the BinarySearch(J[],J,Generic IComparer) method are passed to the ShowWhere generic method, which displays the index value if the string is found, and otherwise the elements the search string would fall between if it were in the array. The index is negative if the string is not n the array, so the ShowWhere method takes the bitwise complement (the ~ operator in C# and Visual C++, Xor -1 in Visual Basic) to obtain the index of the first element in the list that is larger than the search string.

Imports System
Imports System.Collections.Generic

Public Class ReverseComparer
    Implements IComparer(Of String)

    Public Function Compare(ByVal x As String, _
        ByVal y As String) As Integer _
        Implements IComparer(Of String).Compare

        ' Compare y and x in reverse order.
        Return y.CompareTo(x)

    End Function
End Class

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs() As String = { _
            "Pachycephalosaurus", _
            "Amargasaurus", _
            "Tyrannosaurus", _
            "Mamenchisaurus", _
            "Deinonychus", _
            "Edmontosaurus"  }

        For Each dinosaur As String In dinosaurs

        Dim rc As New ReverseComparer()

        Console.WriteLine(vbLf & "Sort")
        Array.Sort(dinosaurs, rc)

        For Each dinosaur As String In dinosaurs

        Console.WriteLine(vbLf & _
            "BinarySearch for 'Coelophysis':")
        Dim index As Integer = _
            Array.BinarySearch(dinosaurs, "Coelophysis", rc)
        ShowWhere(dinosaurs, index)

        Console.WriteLine(vbLf & _
            "BinarySearch for 'Tyrannosaurus':")
        index = Array.BinarySearch(dinosaurs, "Tyrannosaurus", rc)
        ShowWhere(dinosaurs, index)

    End Sub

    Private Shared Sub ShowWhere(Of T) _
        (ByVal array() As T, ByVal index As Integer) 

        If index < 0 Then
            ' If the index is negative, it represents the bitwise
            ' complement of the next larger element in the array.
            index = index Xor -1

            Console.Write("Not found. Sorts between: ")

            If index = 0 Then
                Console.Write("beginning of array and ")
                Console.Write("{0} and ", array(index - 1))
            End If 

            If index = array.Length Then
                Console.WriteLine("end of array.")
                Console.WriteLine("{0}.", array(index))
            End If 
            Console.WriteLine("Found at index {0}.", index)
        End If

    End Sub

End Class

' This code example produces the following output:
'BinarySearch for 'Coelophysis':
'Not found. Sorts between: Deinonychus and Amargasaurus.
'BinarySearch for 'Tyrannosaurus':
'Found at index 0.

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

.NET Compact Framework

Supported in: 2.0

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