Array vs ArrayList in C#

In C#, choosing between an array and an ArrayList depends largely on the specific requirements of the application, such as the need for type safety, size flexibility, or performance considerations. This article compares arrays and ArrayLists in C#, highlighting their differences, advantages, and use cases to help determine when to use each.

Understanding Arrays in C#

An array is a collection of elements that are all of the same type and are stored in contiguous memory locations. Arrays are fixed in size, meaning the number of elements they can hold is set when they are created and cannot be changed afterwards.

Example of Using an Array:

int[] numbers = new int[5] { 1, 2, 3, 4, 5 };
for (int i = 0; i < numbers.Length; i++)
{
    Console.WriteLine(numbers[i]);
}

Understanding ArrayList in C#

ArrayList, part of the System.Collections namespace, is a dynamic array that can hold items of any type. Unlike arrays, ArrayLists can adjust their size dynamically as items are added or removed. However, they require boxing and unboxing when working with value types, which can affect performance.

Example of Using an ArrayList:

ArrayList myArrayList = new ArrayList();
myArrayList.Add(1);    // Integer
myArrayList.Add("two");  // String
myArrayList.Add(3.0);  // Double

foreach (object obj in myArrayList)
{
    Console.WriteLine(obj);
}

Key Differences Between Array and ArrayList

Type Safety: Arrays are type-safe, meaning they store only one specific type of elements. ArrayLists, being non-generic, can store objects of any type, which leads to a lack of type safety.
Performance: Arrays are generally faster than ArrayLists due to their fixed size and type safety. ArrayLists incur overhead from boxing and unboxing operations when storing and retrieving value types.
Size Flexibility: Arrays have a fixed size while ArrayLists can grow or shrink dynamically, providing more flexibility in managing collections of items where the size is not known upfront.

When to Use Array

When you need type safety and want to store only one type of elements.
When the number of elements is known at compile time and is not expected to change.
When performance is a concern, particularly with value types.

When to Use ArrayList

When you need a collection that can change size dynamically.
When you are working with data of various types and can manage type casting explicitly.
In applications where performance is less critical, or the benefit of dynamic resizing outweighs the performance cost of boxing and unboxing.

Conclusion

Choosing between an array and an ArrayList in C# should be based on specific needs such as performance, type safety, and the flexibility of the collection size. While arrays offer better performance and type safety, ArrayLists provide the convenience of dynamic resizing and the ability to store heterogeneous objects.

array vs arraylist in c#