Difference between Areay and ArrayList

A simple explanation is that Array is part of the C# language; it is in the System namespace. ArrayList is in the System.Collections namespace. When possible it is better to use the List class in the System.Collections.Generic namespace. It can be used very much like an ArrayList but has the advantage of type safety.

Array vs ArrayList in .NET Framework. Let’s break it down carefully and clearly, because they look similar but behave very differently.

1. Array

• Definition: A fixed-size, strongly typed collection of elements.

• Namespace: System

• Syntax Example:

int[] numbers = new int[5]; // Array of 5 integers
numbers[0] = 10;

• Characteristics:

  1. Fixed Size – once created, you cannot change the size.

  2. Strongly Typed – all elements must be of the same type (int, string, etc.).

  3. Performance – faster because it’s a simple, contiguous block of memory.

  4. Index-based – access elements using an index: numbers[0].

2. ArrayList

• Definition: A dynamic, non-generic collection of objects.

• Namespace: System.Collections

• Syntax Example:

ArrayList list = new ArrayList();
list.Add(10);        // int
list.Add("Hello");   // string

• Characteristics:

  1. Dynamic Size – you can add or remove elements anytime.

  2. Holds objects of any type – but you lose type safety (you need casting when retrieving values).

     int num = (int)list[0]; // must cast
     

  3. Slower than Array – because elements are stored as objects and boxing/unboxing may occur for value types.

  4. Index-based – like arrays, you can access elements with an index.

3. Key Differences Table

Note

• In modern .NET development, instead of ArrayList, people usually use List (from System.Collections.Generic) because it’s type-safe and dynamic, combining the best of both worlds.

Example:

List list = new List();
list.Add(10);
list.Add(20);

Example:

Array:

int[] numbers = new int[3];
numbers[0] = 1;

ArrayList:

ArrayList list = new ArrayList();
list.Add(1);          // Value type (int) will be boxed
list.Add("hello");    // Stores different types (not type-safe)

Recommendation:

• Use Array for performance-critical, fixed-size, type-safe scenarios.
• Use List (from System.Collections.Generic) instead of ArrayList in modern .NET for better type safety and performance.

Let me know if you want a comparison including List too!