ArrayList.BinarySearch Method (Object)


Searches the entire sorted ArrayList for an element using the default comparer and returns the zero-based index of the element.

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

Public Overridable Function BinarySearch (
	value As Object
) As Integer


Type: System.Object

The Object to locate. The value can be null.

Return Value

Type: System.Int32

The zero-based index of value in the sorted ArrayList, if value is found; otherwise, a negative number, which is the bitwise complement of the index of the next element that is larger than value or, if there is no larger element, the bitwise complement of Count.

Exception Condition

Neither value nor the elements of ArrayList implement the IComparable interface.


value is not of the same type as the elements of the ArrayList.

The value parameter and each element of the ArrayList must implement the IComparable interface, which is used for comparisons. The elements of the ArrayList must already be sorted in increasing value according to the sort order defined by the IComparable implementation; otherwise, the result might be incorrect.

Comparing null with any type is allowed and does not generate an exception when using IComparable. When sorting, null is considered to be less than any other object.

If the ArrayList contains more than one element with the same value, the method returns only one of the occurrences, and it might return any one of the occurrences, not necessarily the first one.

If the ArrayList does not contain the specified value, the method returns a negative integer. You can apply the bitwise complement operation (~) to this negative integer to get the index of the first element that is larger than the search value. When inserting the value into the ArrayList, this index should be used as the insertion point to maintain the sort order.

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

The following code example shows how to use BinarySearch to locate a specific object in the ArrayList.

Imports System
Imports System.Collections
Imports Microsoft.VisualBasic

Public Class SamplesArrayList    

    Public Shared Sub Main()

        ' Creates and initializes a new ArrayList. BinarySearch requires
        ' a sorted ArrayList.
        Dim myAL As New ArrayList()
        Dim i As Integer
        For i = 0 To 4
            myAL.Add(i * 2)
        Next i 

        ' Displays the ArrayList.
        Console.WriteLine("The Int32 ArrayList contains the following:")

        ' Locates a specific object that does not exist in the ArrayList.
        Dim myObjectOdd As Object = 3
        FindMyObject(myAL, myObjectOdd)

        ' Locates an object that exists in the ArrayList.
        Dim myObjectEven As Object = 6
        FindMyObject(myAL, myObjectEven)
    End Sub    

    Public Shared Sub FindMyObject(myList As ArrayList, myObject As Object)
        Dim myIndex As Integer = myList.BinarySearch(myObject)
        If myIndex < 0 Then
            Console.WriteLine("The object to search for ({0}) is not found. " _
               + "The next larger object is at index {1}.", myObject, _
               Not myIndex)
            Console.WriteLine("The object to search for ({0}) is at index " _
               + "{1}.", myObject, myIndex)
        End If
    End Sub

    Public Shared Sub PrintValues(myList As IEnumerable)
        Dim obj As [Object]
        For Each obj In  myList
            Console.Write("   {0}", obj)
        Next obj
    End Sub 'PrintValues

End Class

' This code produces the following output.
' The Int32 ArrayList contains the following:
'     0    2    4    6    8
' The object to search for (3) is not found. The next larger object is at index 2.
' The object to search for (6) is at index 3. 

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
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