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ArrayList.Add Method

Adds an object to the end of the ArrayList.

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

public virtual int Add(
	Object value


Type: System.Object

The Object to be added to the end of the ArrayList. The value can be null.

Return Value

Type: System.Int32
The ArrayList index at which the value has been added.




The ArrayList is read-only.


The ArrayList has a fixed size.

ArrayList accepts null as a valid value and allows duplicate elements.

If Count already equals Capacity, the capacity of the ArrayList is increased by automatically reallocating the internal array, and the existing elements are copied to the new array before the new element is added.

If Count is less than Capacity, this method is an O(1) operation. If the capacity needs to be increased to accommodate the new element, this method becomes an O(n) operation, where n is Count.

The following code example shows how to add elements to the ArrayList.

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

   public static void Main()  {

      // Creates and initializes a new ArrayList.
      ArrayList myAL = new ArrayList();
      myAL.Add( "The" );
      myAL.Add( "quick" );
      myAL.Add( "brown" );
      myAL.Add( "fox" );

      // Creates and initializes a new Queue.
      Queue myQueue = new Queue();
      myQueue.Enqueue( "jumped" );
      myQueue.Enqueue( "over" );
      myQueue.Enqueue( "the" );
      myQueue.Enqueue( "lazy" );
      myQueue.Enqueue( "dog" );

      // Displays the ArrayList and the Queue.
      Console.WriteLine( "The ArrayList initially contains the following:" );
      PrintValues( myAL, '\t' );
      Console.WriteLine( "The Queue initially contains the following:" );
      PrintValues( myQueue, '\t' );

      // Copies the Queue elements to the end of the ArrayList.
      myAL.AddRange( myQueue );

      // Displays the ArrayList.
      Console.WriteLine( "The ArrayList now contains the following:" );
      PrintValues( myAL, '\t' );

   public static void PrintValues( IEnumerable myList, char mySeparator )  {
      foreach ( Object obj in myList )
         Console.Write( "{0}{1}", mySeparator, obj );


This code produces the following output.

The ArrayList initially contains the following:
    The    quick    brown    fox
The Queue initially contains the following:
    jumped    over    the    lazy    dog
The ArrayList now contains the following:
    The    quick    brown    fox    jumped    over    the    lazy    dog

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, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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.

.NET Framework

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

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0