Learn how to create C# ArrayList

ArrayList in C#

ArrayList is a type of non-generic collection framework available in the .Net framework for creating an array of objects list using C# language. The non-generic refers to that we don’t need to mention the data type of the array list. This array list can be dynamically defined of what size wanted. Unlike array initialization, we don’t need to specify the size of the list. It dynamically allocates size as we add or remove an element in the array list. Since it is a non-generic collection, the elements added to the array are stored as an object.

The basic operation we do in ArrayList add, remove, count, sort list. We can also do many operations such as reverse the ArrayList, get the index value of elements etc.

To view full properties and methods please refer: https://docs.microsoft.com/en-us/dotnet/api/system.collections.arraylist?view=netcore-3.1

Create ArrayList

We can create an ArrayList using the ArrayList class and new operator.

using System;
using System.Collections;
					
public class Program
{
	public static void Main()
	{
		//array1 array list is created using new operator.
		ArrayList array1=new ArrayList();
		
	}
}

Add() method

Add(Object value) method will add the element to the ArrayList one after another.

using System;
using System.Collections;
					
public class Program
{
	public static void Main()
	{
		
		ArrayList array1=new ArrayList();
		//adding 5 elements to array1 using ADD() method.
		array1.Add("Element1");
		array1.Add("Element2");
		array1.Add("Element3");
		array1.Add("Element4");
	}
}

Remove()

Remove(Object value) method will remove the element mentioned.

using System;
using System.Collections;
					
public class Program
{
	public static void Main()
	{
		
		ArrayList array1=new ArrayList();
		//adding 5 elements to array1 using Add() method.
		array1.Add("Element1");
		array1.Add("Element2");
		array1.Add("Element3");
		array1.Add("Element4");
		
		Console.WriteLine("Before removing");
		//output of array1 before remove
		foreach(string str in array1)
		{
			Console.WriteLine(str);
		}
		
		//removing Element4 and Element3 from array1 arraylist using Remove().
		array1.Remove("Element3");
		array1.Remove("Element4");
		
		Console.WriteLine("After removing");
		//output of array2 after remove
		foreach(string str in array1)
		{
			Console.WriteLine(str);
		}
		
	}
}

Output:

Before removing
Element1
Element2
Element3
Element4
After removing
Element1
Element2

In the above program, foreach used to iterate through array1 ArrayList to display the elements.

Using indexers [<index_number>] we can access the elements in the array list.

The output shows the elements in array1 before and after remove() method is used.

• To get the no of elements in the ArrayList use Count property.
• To sort the ArrayList use Sort() method.
• To check an element is contained in the ArrayList use Contains() method.

		//get the count of elements in array1
		Console.WriteLine(array1.Count);
		//to sort the array1
		array1.Sort();
		//check element contains in an array and return true if it contains the element else return false
		Console.WriteLine(array1.Contains("Element1"));

Some other methods are

Insert(int index,object value)

• Use to insert the element at the given index.

RemoveAt(int index)

• Removes the element at the given index.

BinarSearch(object value)

• Search for an object using binary search.

Clear()

• Clear all the elements in ArrayList.

IndexOf(object value)

• Gets the index of the particular object.

For other operations refer .NET docs.

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— Developers Doors (@DevelopersDoors) February 3, 2021

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