What’s Wrong with an ArrayList?

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The main problem with ArrayList is that is uses object – it means you have to cast to and from whatever you are encapsulating. It is a remnant of the days before generics and is probably around for backwards compatibility only.

You do not have the type safety with ArrayList that you have with a generic list. The performance issue is in the need to cast objects back to the original (or have implicit boxing happen).

Implicit boxing will happen whenever you use a value type – it will be boxed when put into the ArrayList and unboxed when referenced.

The issue is not just that of performance, but also of readablity and correctness. Since generics came in, this object has become obsolete and would only be needed in .NET 1.0/1.1 code.

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