ArrayList Class (System.Collections)

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Microsoft Visual Studio 2008/.NET Framework 3.5

Other versions are also available for the following:

.NET Framework Class Library

ArrayList Class

Updated: November 2007

Implements the IList interface using an array whose size is dynamically increased as required.

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

Syntax

Visual Basic (Declaration)

<SerializableAttribute> _
<ComVisibleAttribute(True)> _
Public Class ArrayList _
    Implements IList, ICollection, IEnumerable, ICloneable

Visual Basic (Usage)

Dim instance As ArrayList

[SerializableAttribute]
[ComVisibleAttribute(true)]
public class ArrayList : IList, ICollection, 
    IEnumerable, ICloneable

Visual C++

[SerializableAttribute]
[ComVisibleAttribute(true)]
public ref class ArrayList : IList, 
    ICollection, IEnumerable, ICloneable

/** @attribute SerializableAttribute */ 
/** @attribute ComVisibleAttribute(true) */
public class ArrayList implements IList, 
    ICollection, IEnumerable, ICloneable

JScript

public class ArrayList implements IList, ICollection, IEnumerable, ICloneable

Remarks

The ArrayList is not guaranteed to be sorted. You must sort the ArrayList prior to performing operations (such as BinarySearch) that require the ArrayList to be sorted.

The capacity of a ArrayList is the number of elements the ArrayList can hold. As elements are added to a ArrayList, the capacity is automatically increased as required through reallocation. The capacity can be decreased by calling TrimToSize or by setting the Capacity property explicitly.

Elements in this collection can be accessed using an integer index. Indexes in this collection are zero-based.

ArrayList accepts nullNothingnullptra null reference (Nothing in Visual Basic) as a valid value and allows duplicate elements.

Examples

The following code example shows how to create and initialize an ArrayList and how to print out its values.

Visual Basic

Imports System
Imports System.Collections
Imports Microsoft.VisualBasic

Public Class SamplesArrayList    

    Public Shared Sub Main()

        ' Creates and initializes a new ArrayList.
        Dim myAL As New ArrayList()
        myAL.Add("Hello")
        myAL.Add("World")
        myAL.Add("!")

        ' Displays the properties and values of the ArrayList.
        Console.WriteLine("myAL")
        Console.WriteLine("    Count:    {0}", myAL.Count)
        Console.WriteLine("    Capacity: {0}", myAL.Capacity)
        Console.Write("    Values:")
        PrintValues(myAL)
    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 output similar to the following:
' 
' myAL
'     Count:    3
'     Capacity: 4
'     Values:   Hello   World   !

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

   public static void Main()  {

      // Creates and initializes a new ArrayList.
      ArrayList myAL = new ArrayList();
      myAL.Add("Hello");
      myAL.Add("World");
      myAL.Add("!");

      // Displays the properties and values of the ArrayList.
      Console.WriteLine( "myAL" );
      Console.WriteLine( "    Count:    {0}", myAL.Count );
      Console.WriteLine( "    Capacity: {0}", myAL.Capacity );
      Console.Write( "    Values:" );
      PrintValues( myAL );
   }

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

}


/* 
This code produces output similar to the following:

myAL
    Count:    3
    Capacity: f
    Values:   Hello   World   !

*/

Visual C++

using namespace System;
using namespace System::Collections;
void PrintValues( IEnumerable^ myList );
int main()
{

   // Creates and initializes a new ArrayList.
   ArrayList^ myAL = gcnew ArrayList;
   myAL->Add( "Hello" );
   myAL->Add( "World" );
   myAL->Add( "!" );

   // Displays the properties and values of the ArrayList.
   Console::WriteLine( "myAL" );
   Console::WriteLine( "    Count:    {0}", myAL->Count );
   Console::WriteLine( "    Capacity: {0}", myAL->Capacity );
   Console::Write( "    Values:" );
   PrintValues( myAL );
}

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 output similar to the following:

myAL
    Count:    3
    Capacity: 4
    Values:   Hello   World   !

*/

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

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

        myAL.Add("Hello");
        myAL.Add("World");
        myAL.Add("!");

        // Displays the properties and values of the ArrayList.
        Console.WriteLine("myAL");
        Console.WriteLine("    Count:    {0}", (Int32)myAL.get_Count());
        Console.WriteLine("    Capacity: {0}", (Int32)myAL.get_Capacity());
        Console.Write("    Values:");
        PrintValues(myAL);
    } //main

    public static void PrintValues(IEnumerable myList)
    {
        IEnumerator objMyEnum = myList.GetEnumerator();
        while (objMyEnum.MoveNext()) {
            Object obj = objMyEnum.get_Current();
            Console.Write("   {0}", obj);
        }
        Console.WriteLine();
    } //PrintValues
} //SamplesArrayList 
/* 
 This code produces output similar to the following:

 myAL
     Count:    3
     Capacity: 4
     Values:   Hello   World   !

 */

JScript

import System;
import System.Collections;

// Creates and initializes a new ArrayList.
var myAL : ArrayList = new ArrayList();
myAL.Add("Hello");
myAL.Add("World");
myAL.Add("!");

// Displays the properties and values of the ArrayList.
Console.WriteLine( "myAL" );
Console.WriteLine( "\tCount:    {0}", myAL.Count );
Console.WriteLine( "\tCapacity: {0}", myAL.Capacity );
Console.Write( "\tValues:" );
PrintValues( myAL );


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 output similar to the following:

 myAL
     Count:    3
     Capacity: 4
     Values:    Hello    World    !
 */

Inheritance Hierarchy

System..::.Object
System.Collections..::.ArrayList
System.Windows.Forms..::.DomainUpDown..::.DomainUpDownItemCollection

Thread Safety

Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

An ArrayList can support multiple readers concurrently, as long as the collection is not modified. To guarantee the thread safety of the ArrayList, all operations must be done through the wrapper returned by the Synchronized method.

Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

Platforms

Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, 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

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