How to create the ArrayList in C#

ArrayList() constructor is used to initialize a new instance of the ArrayList class which will be empty and will have the default initial capacity. ArrayList represents an ordered collection of an object that can be indexed individually. It is basically an alternative to an array. It also allows dynamic memory allocation, adding, searching and sorting items in the list.

Syntax:

public ArrayList ();

Important Points:

• The number of elements that an ArrayList can hold is known as the Capacity of the ArrayList. If the elements will be added to the ArrayList then capacity will be automatically increased by reallocating the internal array.
• Specifying the initial capacity will eliminate the requirement to perform a number of resizing operations while adding elements to the ArrayList if the size of the collection can be estimated.
• This constructor is an O(1) operation.

Example 1:

// C# Program to illustrate how
// to create a ArrayList
using System;
using System.Collections;

class Geeks {

    // Main Method
    public static void Main(String[] args)
    {

        // arrlist is the ArrayList object
        // ArrayList() is the constructor
        // used to initializes a new
        // instance of the ArrayList class
        ArrayList arrlist = new ArrayList();

        // Count property is used to get the
        // number of elements in ArrayList
        // It will give 0 as no elements
        // are present currently
        Console.WriteLine(arrlist.Count);
    }
}

Output:

0

Example 2:

// C# Program to illustrate how
// to create a ArrayList
using System;
using System.Collections;

class Geeks {

    // Main Method
    public static void Main(String[] args)
    {

        // arrlist is the ArrayList object
        // ArrayList() is the constructor
        // used to initializes a new
        // instance of the ArrayList class
        ArrayList arrlist = new ArrayList();

        Console.Write("Before Add Method: ");

        // Count property is used to get the
        // number of elements in ArrayList
        // It will give 0 as no elements
        // are present currently
        Console.WriteLine(arrlist.Count);

        // Adding the elements
        // to the ArrayList
        arrlist.Add("This");
        arrlist.Add("is");
        arrlist.Add("C#");
        arrlist.Add("ArrayList");

        Console.Write("After Add Method: ");

        // Count property is used to get the
        // number of elements in arrlist
        Console.WriteLine(arrlist.Count);
    }
}

Output:

Before Add Method: 0
After Add Method: 4

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.arraylist.-ctor?view=netframework-4.7.2#System_Collections_ArrayList__ctor