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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 virtual int BinarySearch (
	Object value
)
public int BinarySearch (
	Object value
)
public function BinarySearch (
	value : Object
) : int
Not applicable.

Parameters

value

The Object to locate. The value can be a null reference (Nothing in Visual Basic).

Return Value

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 typeCondition

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.

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

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

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.
*/ 

import System.*;
import System.Collections.*;

public class SamplesArrayList
{
    public static void main(String[] args)
    {
        // Creates and initializes a new ArrayList.
        ArrayList myAL = new ArrayList();

        for (int i = 0; i <= 4; i++) {
            myAL.Add(System.Convert.ToString(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 = new String("3");
        FindMyObject(myAL, myObjectOdd);

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

    public static void FindMyObject(ArrayList myList, Object myObject)
    {
        int myIndex = 
            myList.BinarySearch(myObject.toString());

        if (myIndex < 0) {
            Console.WriteLine("The object to search for ({0}) is not found."
                + " The next larger object is at index {1}.", myObject, 
                System.Convert.ToString(~myIndex));
        }
        else {
            Console.WriteLine("The object to search for ({0}) is at index {1}.",
                myObject, System.Convert.ToString(myIndex));
        }
    } //FindMyObject

    public static void PrintValues(IEnumerable myList)
    {
        IEnumerator objEnum = myList.GetEnumerator();
        while (objEnum.MoveNext()) {
            Object obj = objEnum.get_Current();
            Console.Write("   {0}", obj);
        }
        Console.WriteLine();
    } //PrintValues
} //SamplesArrayList 
/* 
 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.
 */

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.
 */ 

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

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0
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