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ArrayList.IndexOf Method (Object)

Searches for the specified Object and returns the zero-based index of the first occurrence within the entire ArrayList.

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

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

Parameters

value

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

Return Value

The zero-based index of the first occurrence of value within the entire ArrayList, if found; otherwise, -1.

The ArrayList is searched forward starting at the first element and ending at the last element.

This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

This method determines equality by calling Object.Equals.

Starting with the .NET Framework 2.0, this method uses the collection’s objects’ Equals and CompareTo methods on item to determine whether item exists. In the earlier versions of the .NET Framework, this determination was made by using the Equals and CompareTo methods of the item parameter on the objects in the collection.

The following code example shows how to determine the index of the first occurrence of a specified element.

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

    public static void Main()  
    {
 
        // Creates and initializes a new ArrayList with three elements of the same value.
        ArrayList myAL = new ArrayList();
        myAL.Add( "the" );
        myAL.Add( "quick" );
        myAL.Add( "brown" );
        myAL.Add( "fox" );
        myAL.Add( "jumps" );
        myAL.Add( "over" );
        myAL.Add( "the" );
        myAL.Add( "lazy" );
        myAL.Add( "dog" );
        myAL.Add( "in" );
        myAL.Add( "the" );
        myAL.Add( "barn" );

        // Displays the values of the ArrayList.
        Console.WriteLine( "The ArrayList contains the following values:" );
        PrintIndexAndValues( myAL );

        // Search for the first occurrence of the duplicated value.
        String myString = "the";
        int myIndex = myAL.IndexOf( myString );
        Console.WriteLine( "The first occurrence of \"{0}\" is at index {1}.", myString, myIndex );

        // Search for the first occurrence of the duplicated value in the last section of the ArrayList.
        myIndex = myAL.IndexOf( myString, 4 );
        Console.WriteLine( "The first occurrence of \"{0}\" between index 4 and the end is at index {1}.", myString, myIndex );

        // Search for the first occurrence of the duplicated value in a section of the ArrayList.
        myIndex = myAL.IndexOf( myString, 6, 6 );
        Console.WriteLine( "The first occurrence of \"{0}\" between index 6 and index 11 is at index {1}.", myString, myIndex );

        // Search for the first occurrence of the duplicated value in a small section at the end of the ArrayList.
        myIndex = myAL.IndexOf( myString, 11 );
        Console.WriteLine( "The first occurrence of \"{0}\" between index 11 and the end is at index {1}.", myString, myIndex );
    }

    public static void PrintIndexAndValues(IEnumerable myList)
    {
        int i = 0;
        foreach (Object obj in myList)
            Console.WriteLine("   [{0}]:    {1}", i++, obj);
        Console.WriteLine();
    }

}
/* 
This code produces output similar to the following:
 
The ArrayList contains the following values:
   [0]:    the
   [1]:    quick
   [2]:    brown
   [3]:    fox
   [4]:    jumps
   [5]:    over
   [6]:    the
   [7]:    lazy
   [8]:    dog
   [9]:    in
   [10]:    the
   [11]:    barn

The first occurrence of "the" is at index 0.
The first occurrence of "the" between index 4 and the end is at index 6.
The first occurrence of "the" between index 6 and index 11 is at index 6.
The first occurrence of "the" between index 11 and the end is at index -1.
*/

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

public class SamplesArrayList
{
    public static void main(String[] args)
    {
        // Creates and initializes a new ArrayList with three elements of the
        // same value.
        ArrayList myAL = new ArrayList();
        myAL.Add("the");
        myAL.Add("quick");
        myAL.Add("brown");
        myAL.Add("fox");
        myAL.Add("jumps");
        myAL.Add("over");
        myAL.Add("the");
        myAL.Add("lazy");
        myAL.Add("dog");
        myAL.Add("in");
        myAL.Add("the");
        myAL.Add("barn");

        // Displays the values of the ArrayList.
        Console.WriteLine("The ArrayList contains the following values:");
        PrintIndexAndValues(myAL);

        // Search for the first occurrence of the duplicated value.
        String myString = "the";
        int myIndex = myAL.IndexOf(myString);

        Console.WriteLine("The first occurrence of \"{0}\" is at index {1}.",
            myString, (Int32)myIndex);

        // Search for the first occurrence of the duplicated value in the 
        // last section of the ArrayList.
        myIndex = myAL.IndexOf(myString, 4);
        Console.WriteLine("The first occurrence of \"{0}\" between index 4"
            + " and the end is at index {1}.", myString, (Int32)myIndex);

        // Search for the first occurrence of the duplicated value in a 
        // section of the ArrayList.
        myIndex = myAL.IndexOf(myString, 6, 6);
        Console.WriteLine("The first occurrence of \"{0}\" between index 6"
            + " and index 11 is at index {1}.", myString, (Int32)myIndex);
    } //main

    public static void PrintIndexAndValues(IEnumerable myList)
    {
        int i = 0;
        IEnumerator objMyEnum = myList.GetEnumerator();
        while (objMyEnum.MoveNext()) {
            Object obj = objMyEnum.get_Current();
            Console.WriteLine("   [{0}]:    {1}", (Int32)i++, obj);
        }
        Console.WriteLine();
    } //PrintIndexAndValues
} //SamplesArrayList 
/* 
 This code produces the following output.
 
 The ArrayList contains the following values:
    [0]:    the
    [1]:    quick
    [2]:    brown
    [3]:    fox
    [4]:    jumps
    [5]:    over
    [6]:    the
    [7]:    lazy
    [8]:    dog
    [9]:    in
    [10]:    the
    [11]:    barn

 The first occurrence of "the" is at index 0.
 The first occurrence of "the" between index 4 and the end is at index 6.
 The first occurrence of "the" between index 6 and index 11 is at index 6.
 */

import System;
import System.Collections;


// Creates and initializes a new ArrayList with three elements of the same value.
var myAL : ArrayList  = new ArrayList();
myAL.Add( "the" );
myAL.Add( "quick" );
myAL.Add( "brown" );
myAL.Add( "fox" );
myAL.Add( "jumped" );
myAL.Add( "over" );
myAL.Add( "the" );
myAL.Add( "lazy" );
myAL.Add( "dog" );
myAL.Add( "in" );
myAL.Add( "the" );
myAL.Add( "barn" );

// Displays the values of the ArrayList.
Console.WriteLine( "The ArrayList contains the following values:" );
PrintIndexAndValues( myAL );

// Search for the first occurrence of the duplicated value.
var myString : String = "the";
var myIndex : int = myAL.IndexOf( myString );
Console.WriteLine( "The first occurrence of \"{0}\" is at index {1}.", myString, myIndex );

// Search for the first occurrence of the duplicated value in the last section of the ArrayList.
myIndex = myAL.IndexOf( myString, 4 );
Console.WriteLine( "The first occurrence of \"{0}\" between index 4 and the end is at index {1}.", myString, myIndex );

// Search for the first occurrence of the duplicated value in a section of the ArrayList.
myIndex = myAL.IndexOf( myString, 6, 6 );
Console.WriteLine( "The first occurrence of \"{0}\" between index 6 and index 11 is at index {1}.", myString, myIndex );


function PrintIndexAndValues( myList : IEnumerable)  {
   var i : int = 0;
   var myEnumerator : System.Collections.IEnumerator  = myList.GetEnumerator();
   while ( myEnumerator.MoveNext() )
      Console.WriteLine( "\t[{0}]:\t{1}", i++, myEnumerator.Current );
   Console.WriteLine();
}

 /* 
 This code produces the following output.
 
 The ArrayList contains the following values:
     [0]:    the
     [1]:    quick
     [2]:    brown
     [3]:    fox
     [4]:    jumped
     [5]:    over
     [6]:    the
     [7]:    lazy
     [8]:    dog
     [9]:    in
     [10]:    the
     [11]:    barn
 
 The first occurrence of "the" is at index 0.
 The first occurrence of "the" between index 4 and the end is at index 6.
 The first occurrence of "the" between index 6 and index 11 is at index 6.
 */ 

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

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0

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