ArrayList Class

Definition

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

[System.Runtime.InteropServices.ComVisible(true)]
public class ArrayList : ICloneable, System.Collections.IList
Inheritance
ArrayList
Derived
Attributes
Implements

Inherited Members

System.Object

Examples

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

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   !

*/
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: 4
    Values:   Hello   World   !

*/
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   !

Remarks

Note

To view the .NET Framework source code for this type, see the Reference Source. You can browse through the source code online, download the reference for offline viewing, and step through the sources (including patches and updates) during debugging; see instructions.

The ArrayList class is designed to hold heterogeneous collections of objects. However, it does not always offer the best performance. Instead, we recommend the following:

  • For a heterogeneous collection of objects, use the List<Object> (in C#) or List(Of Object) (in Visual Basic) type.

  • For a homogeneous collection of objects, use the List<T> class.

See the "Performance Considerations" section in the List<T> reference topic for a discussion of the relative performance of these classes.

The ArrayList is not guaranteed to be sorted. You must sort the ArrayList by calling its Sort method prior to performing operations (such as BinarySearch) that require the ArrayList to be sorted. To maintain a collection that is automatically sorted as new elements are added, you can use the SortedSet<T> class.

The capacity of an ArrayList is the number of elements the ArrayList can hold. As elements are added to an 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.

For very large ArrayList objects, you can increase the maximum capacity to 2 billion elements on a 64-bit system by setting the enabled attribute of the configuration element to true in the run-time environment.

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

The ArrayList collection accepts null as a valid value. It also allows duplicate elements.

Using multidimensional arrays as elements in an ArrayList collection is not supported.

Constructors

ArrayList()

Initializes a new instance of the ArrayList class that is empty and has the default initial capacity.

ArrayList(ICollection)

Initializes a new instance of the ArrayList class that contains elements copied from the specified collection and that has the same initial capacity as the number of elements copied.

ArrayList(Int32)

Initializes a new instance of the ArrayList class that is empty and has the specified initial capacity.

Properties

Capacity

Gets or sets the number of elements that the ArrayList can contain.

Count

Gets the number of elements actually contained in the ArrayList.

IsFixedSize

Gets a value indicating whether the ArrayList has a fixed size.

IsReadOnly

Gets a value indicating whether the ArrayList is read-only.

IsSynchronized

Gets a value indicating whether access to the ArrayList is synchronized (thread safe).

Item[Int32]

Gets or sets the element at the specified index.

SyncRoot

Gets an object that can be used to synchronize access to the ArrayList.

Methods

Adapter(IList)

Creates an ArrayList wrapper for a specific IList.

Add(Object)

Adds an object to the end of the ArrayList.

AddRange(ICollection)

Adds the elements of an ICollection to the end of the ArrayList.

BinarySearch(Object)

Searches the entire sorted ArrayList for an element using the default comparer and returns the zero-based index of the element.

BinarySearch(Object, IComparer)

Searches the entire sorted ArrayList for an element using the specified comparer and returns the zero-based index of the element.

BinarySearch(Int32, Int32, Object, IComparer)

Searches a range of elements in the sorted ArrayList for an element using the specified comparer and returns the zero-based index of the element.

Clear()

Removes all elements from the ArrayList.

Clone()

Creates a shallow copy of the ArrayList.

Contains(Object)

Determines whether an element is in the ArrayList.

CopyTo(Array)

Copies the entire ArrayList to a compatible one-dimensional Array, starting at the beginning of the target array.

CopyTo(Array, Int32)

Copies the entire ArrayList to a compatible one-dimensional Array, starting at the specified index of the target array.

CopyTo(Int32, Array, Int32, Int32)

Copies a range of elements from the ArrayList to a compatible one-dimensional Array, starting at the specified index of the target array.

FixedSize(ArrayList)

Returns an ArrayList wrapper with a fixed size.

FixedSize(IList)

Returns an IList wrapper with a fixed size.

GetEnumerator()

Returns an enumerator for the entire ArrayList.

GetEnumerator(Int32, Int32)

Returns an enumerator for a range of elements in the ArrayList.

GetRange(Int32, Int32)

Returns an ArrayList which represents a subset of the elements in the source ArrayList.

IndexOf(Object)

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

IndexOf(Object, Int32)

Searches for the specified Object and returns the zero-based index of the first occurrence within the range of elements in the ArrayList that extends from the specified index to the last element.

IndexOf(Object, Int32, Int32)

Searches for the specified Object and returns the zero-based index of the first occurrence within the range of elements in the ArrayList that starts at the specified index and contains the specified number of elements.

Insert(Int32, Object)

Inserts an element into the ArrayList at the specified index.

InsertRange(Int32, ICollection)

Inserts the elements of a collection into the ArrayList at the specified index.

LastIndexOf(Object)

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

LastIndexOf(Object, Int32)

Searches for the specified Object and returns the zero-based index of the last occurrence within the range of elements in the ArrayList that extends from the first element to the specified index.

LastIndexOf(Object, Int32, Int32)

Searches for the specified Object and returns the zero-based index of the last occurrence within the range of elements in the ArrayList that contains the specified number of elements and ends at the specified index.

ReadOnly(ArrayList)

Returns a read-only ArrayList wrapper.

ReadOnly(IList)

Returns a read-only IList wrapper.

Remove(Object)

Removes the first occurrence of a specific object from the ArrayList.

RemoveAt(Int32)

Removes the element at the specified index of the ArrayList.

RemoveRange(Int32, Int32)

Removes a range of elements from the ArrayList.

Repeat(Object, Int32)

Returns an ArrayList whose elements are copies of the specified value.

Reverse()

Reverses the order of the elements in the entire ArrayList.

Reverse(Int32, Int32)

Reverses the order of the elements in the specified range.

SetRange(Int32, ICollection)

Copies the elements of a collection over a range of elements in the ArrayList.

Sort()

Sorts the elements in the entire ArrayList.

Sort(IComparer)

Sorts the elements in the entire ArrayList using the specified comparer.

Sort(Int32, Int32, IComparer)

Sorts the elements in a range of elements in ArrayList using the specified comparer.

Synchronized(ArrayList)

Returns an ArrayList wrapper that is synchronized (thread safe).

Synchronized(IList)

Returns an IList wrapper that is synchronized (thread safe).

ToArray()

Copies the elements of the ArrayList to a new Object array.

ToArray(Type)

Copies the elements of the ArrayList to a new array of the specified element type.

TrimToSize()

Sets the capacity to the actual number of elements in the ArrayList.

Extension Methods

Cast<TResult>(IEnumerable)
OfType<TResult>(IEnumerable)
AsParallel(IEnumerable)
AsQueryable(IEnumerable)

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(IList) 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.