Array vs ArrayList in C#

#csharp #array #arraylist

In C#, both Arrays and ArrayLists are used to store collections of data, but they have some differences in terms of their characteristics and usage.

Declaration

Arrays are fixed-size collections of items that are declared with a specific size and type at the time of creation.
ArrayLists are dynamically-sized collections that can grow or shrink in size.

Initialization

Arrays can have multiple dimensions (multi-dimensional arrays) or just one dimension (single-dimensional arrays).
ArrayLists are not type-specific. They can store items of any type.

Memory Allocation

Arrays are allocated in contiguous memory locations.
ArrayLists are allocated in heap memory, which can result in memory fragmentation and slower performance compared to arrays.

Performance

Arrays offer better performance in terms of access time and memory usage compared. Arrays have a fixed size and a direct memory layout, which allows for faster indexing and retrieval of items.
ArrayLists may require boxing and unboxing operations for value types, which can result in performance overhead.

Type Safety

Arrays are statically typed, meaning that they have a fixed type that is known at compile-time.
ArrayLists are dynamically typed, allowing for items of any type to be added. This can result in runtime errors if the wrong type of item is accessed from an ArrayList.

Flexibility

Arrays have fixed sizes and require manual resizing and manipulation.
ArrayLists offer more flexibility compared, as they can grow or shrink dynamically during runtime. ArrayLists also provide additional methods for inserting, removing, and manipulating items.

Usage

Arrays are commonly used when you need a fixed-size collection of items with a known type, and performance is a critical factor, such as when dealing with large datasets or performance-critical applications.
ArrayLists are useful when you need a dynamic-sized collection that can grow or shrink during runtime and when you need to store items of different types.

In general, arrays are more efficient in terms of performance and memory usage, but they have fixed sizes and are statically typed. ArrayLists, on the other hand, offer more flexibility but may have performance overhead and potential type-safety issues.
The choice between Arrays and ArrayLists depends on the specific requirements of your application and the trade-offs between performance, flexibility, and type safety.

Top comments (5)

Anthony Fung • Apr 11 '23

According to the official documentation, it's probably not a good idea to use ArrayLists anymore:

We don't recommend that you use the ArrayList class for new development. Instead, we recommend that you use the generic List class. 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 (in C#) or List(Of Object) (in Visual Basic) type.
For a homogeneous collection of objects, use the List class. See Performance Considerations in the List reference topic for a discussion of the relative performance of these classes. See Non-generic collections shouldn't be used on GitHub for general information on the use of generic instead of non-generic collection types.

Also, I believe that both Arrays and ArrayLists (or Lists) are allocated on the heap. However, arrays will use a contiguous memory block, meaning they are potentially more performant (as mentioned in the article).