.NET Q & A


What is the difference between List and ArrayList in .NET?

In .NET, both List and ArrayList are collections used to store and manipulate groups of related objects. While they serve similar purposes, there are key differences between the two that impact their usage and performance.




List: List is a generic collection introduced in .NET Framework 2.0 that allows you to specify the type of elements it will contain at compile time. This provides strong type-safety, ensuring that only objects of the specified type can be added to the list.

ArrayList: ArrayList, on the other hand, is a non-generic collection introduced in earlier versions of the .NET framework. It can hold objects of any type, allowing for flexibility but sacrificing type-safety. As a result, developers must manually cast objects retrieved from an ArrayList to their appropriate type, which can lead to runtime errors if done incorrectly.




List: Due to its type-safe nature, List typically offers better performance compared to ArrayList. Since List operates on a specific type, it avoids the overhead of boxing and unboxing values (i.e., converting value types to reference types and vice versa) that ArrayList incurs when storing objects of different types.

ArrayList: ArrayList, being non-generic, requires boxing and unboxing operations when storing and retrieving value types, which can impact performance, especially in scenarios where large numbers of elements are involved.


Compile-Time Checking:


List: List provides compile-time checking of the type of elements being added and retrieved, ensuring type safety and reducing the likelihood of runtime errors.

ArrayList: ArrayList does not provide compile-time type checking, which increases the risk of type-related errors at runtime.


Generics Support:


List: List is part of the generic collections introduced in .NET Framework 2.0, making use of generics to provide type safety and improve performance.

ArrayList: ArrayList predates generics and does not benefit from the type safety and performance improvements introduced by generic collections.


While both List and ArrayList are used for storing collections of objects in .NET, List provides stronger type safety, better performance, and compile-time checking compared to ArrayList. Therefore, List is generally preferred in modern .NET development unless compatibility with legacy code or framework versions necessitates the use of ArrayList.

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