ASP.NET C# Lists Which and When?

Question

In C# There seem to be quite a few different lists. Off the top of my head I was able to come up with a couple, however I'm sure there are many more.

List<String> Types = new List<String>();
ArrayList Types2 = new ArrayList();
LinkedList<String> Types4 = new LinkedList<String>();

My question is when is it beneficial to use one over the other?

More specifically I am returning lists of unknown size from functions and I was wondering if there is a particular list that was better at this.

Answer 1

Generally, use List. Don't use ArrayList; it's obsolete. Use LinkedList in the rare cases where you need to be able to add without resizing and don't mind the overhead and loss of random access.

Answer 2

List<String> Types = new List<String>();
LinkedList<String> Types4 = new LinkedList<String>();

are generic lists, i.e. you define the data type that would go in there which decreased boxing and un-boxing.

for difference in list vs linklist, see this --> http://stackoverflow.com/questions/169973/when-should-i-use-a-list-vs-a-linkedlist

ArrayList is a non-generic collection, which can be used to store any type of data type.

Answer 3

ArrayList is probably smaller, memory-wise, since it is based on an array. It also has fast random-access to elements. However, adding or removing to the list will take longer. This might be sped up slightly if the object over-allocates under the assumption that you are going to keep adding. (That will, of course, reduce the memory advantage.)

The other lists will be slightly larger (4-to-8 bytes more memory per element), and will have poor random access times. However, it is very fast to add or remove objects to the ends of the list. Also, memory usage is usually spot-on for what you need.

Answer 4

See the article on Commonly Used Collection Types from MSDN for a list of the the various types of collections available to you, and their intended uses.

Answer 5

99% of the time List is what you'll want. Avoid the non-generic collections at all costs.

LinkedList is useful for adding or removing without shuffling items around, although you have to forego random access as a result. One advantage it does have is you can remove items whilst iterating through the nodes.

Answer 6

ArrayList is a holdover from before Generics. There's really no reason to use them ... they're slow and use more memory than List<>. In general, there's probably no reason to use LinkedList either unless you are inserting midway through VERY large lists.

The only thing you'll find in .NET faster than a List<> is a fixed array ... but the performance difference is surprisingly small.

Answer 7

ArrayList is a .Net 1.0 list type. List is a generic list introduced with generics in .Net 2.0.

Generic lists provide better compile time support. Generics lists are type safe. You cannot add objects of wrong type. Therefor you know which type the stored objects has. There are no typechecks and typecasts nessecary.

I dont know about performance differences.

This questions says something about the difference of List and LinkedList.

Answer 8

As mentioned, don't use ArrayList if at all possible.

Here's an bit on Wikipedia about the differences between arrays and linked lists.

In summary:

Arrays

• Fast random access
• Fast inserting/deleting at end
• Good memory locality

Linked Lists

• Fast inserting/deleting at beginning
• Fast inserting/deleting at end
• Fast inserting/deleting at middle (with enumerator)