ArrayList.BinarySearch Method (Object) (System.Collections)

Microsoft Developer Network

BinarySearch Method (Object)

.NET Framework Class Library

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)

Syntax

Visual Basic (Declaration)

Public Overridable Function BinarySearch ( _
    value As Object _
) As Integer

Visual Basic (Usage)

Dim instance As ArrayList
Dim value As Object
Dim returnValue As Integer

returnValue = instance.BinarySearch(value)

public virtual int BinarySearch(
    Object value
)

Visual C++

public:
virtual int BinarySearch(
    Object^ value
)

JScript

public function BinarySearch(
    value : Object
) : int

Parameters

value: Type: System..::.Object
The Object to locate. The value can be nullNothingnullptra null reference (Nothing in Visual Basic).

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.

Exceptions

Exception	Condition
ArgumentException	Neither value nor the elements of ArrayList implement the IComparable interface.
InvalidOperationException	value is not of the same type as the elements of the ArrayList.

Remarks

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 nullNothingnullptra null reference (Nothing in Visual Basic) with any type is allowed and does not generate an exception when using IComparable. When sorting, nullNothingnullptra null reference (Nothing in Visual Basic) 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.

Examples

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

Visual Basic

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:")
        PrintValues(myAL)

        ' 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)
        Else
            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
        Console.WriteLine()
    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.

using System;
using System.Collections;
public class SamplesArrayList  {

   public static void Main()  {

      // Creates and initializes a new ArrayList. BinarySearch requires
      // a sorted ArrayList.
      ArrayList myAL = new ArrayList();
      for ( int i = 0; i <= 4; i++ )
         myAL.Add( i*2 );

      // Displays the ArrayList.
      Console.WriteLine( "The Int32 ArrayList contains the following:" );
      PrintValues( myAL );

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

      // Locates an object that exists in the ArrayList.
      Object myObjectEven = 6;
      FindMyObject( myAL, myObjectEven );
   }

   public static void FindMyObject( ArrayList myList, Object myObject )  {
      int myIndex=myList.BinarySearch( myObject );
      if ( myIndex < 0 )
         Console.WriteLine( "The object to search for ({0}) is not found. The next larger object is at index {1}.", myObject, ~myIndex );
      else
         Console.WriteLine( "The object to search for ({0}) is at index {1}.", myObject, myIndex );
   }

   public static void PrintValues( IEnumerable myList )  {
      foreach ( Object obj in myList )
         Console.Write( "   {0}", obj );
      Console.WriteLine();
   }

}
/* 
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.
*/

Visual C++

using namespace System;
using namespace System::Collections;
void FindMyObject( ArrayList^ myList, Object^ myObject );
void PrintValues( IEnumerable^ myList );
int main()
{

   // Creates and initializes a new ArrayList. BinarySearch requires
   // a sorted ArrayList.
   ArrayList^ myAL = gcnew ArrayList;
   for ( int i = 0; i <= 4; i++ )
      myAL->Add( i * 2 );

   // Displays the ArrayList.
   Console::WriteLine( "The Int32 ArrayList contains the following:" );
   PrintValues( myAL );

   // Locates a specific object that does not exist in the ArrayList.
   Object^ myObjectOdd = 3;
   FindMyObject( myAL, myObjectOdd );

   // Locates an object that exists in the ArrayList.
   Object^ myObjectEven = 6;
   FindMyObject( myAL, myObjectEven );
}

void FindMyObject( ArrayList^ myList, Object^ myObject )
{
   int myIndex = myList->BinarySearch( myObject );
   if ( myIndex < 0 )
      Console::WriteLine( "The object to search for ({0}) is not found. The next larger object is at index {1}.", myObject,  ~myIndex );
   else
      Console::WriteLine( "The object to search for ({0}) is at index {1}.", myObject, myIndex );
}

void PrintValues( IEnumerable^ myList )
{
   IEnumerator^ myEnum = myList->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      Object^ obj = safe_cast<Object^>(myEnum->Current);
      Console::Write( "   {0}", obj );
   }

   Console::WriteLine();
}

/* 
 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.
 */

JScript

import System;
import System.Collections;


// Creates and initializes a new ArrayList. BinarySearch requires
// a sorted ArrayList.
var myAL : ArrayList = new ArrayList();
for ( var i : int = 0; i <= 4; i++ )
  myAL.Add( int(i*2 ));

// Displays the ArrayList.
Console.WriteLine( "The Int32 ArrayList contains the following:" );
PrintValues( myAL );

// Locates a specific object that does not exist in the ArrayList.
var myObjectOdd = 3;
FindMyObject( myAL, myObjectOdd );

// Locates an object that exists in the ArrayList.
var  myObjectEven = 6;
FindMyObject( myAL, myObjectEven );


function FindMyObject( myList : ArrayList, myObject )  {
   var myIndex : int = myList.BinarySearch( myObject );
   if ( myIndex < 0 )
      Console.WriteLine( "The object to search for ({0}) is not found. The next larger object is at index {1}.", myObject, ~myIndex );
   else
      Console.WriteLine( "The object to search for ({0}) is at index {1}.", myObject, myIndex );
}

function PrintValues( myList : IEnumerable)  {
   var myEnumerator : System.Collections.IEnumerator = myList.GetEnumerator();
   while ( myEnumerator.MoveNext() )
      Console.Write( "\t{0}", myEnumerator.Current );
   Console.WriteLine();
}
 /* 
 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.
 */

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

Reference

ArrayList Class

ArrayList Members

BinarySearch Overload

System.Collections Namespace

Other Resources

Performing Culture-Insensitive String Operations in Collections