Best way to get value from Collection by index

Question

What is the best way to get value from java.util.Collection by index?

Answer 1

Convert the collection into an array by using function

Object[] toArray(Object[] a) 

Answer 2

I agree that this is generally a bad idea. However, Commons Collections had a nice routine for getting the value by index if you really need to:

CollectionUtils.get(collection, index)

Answer 3

You must either wrap your collection in a list (new ArrayList(c)) or use c.toArray() since Collections have no notion of "index" or "order".

Answer 4

I agree with Matthew Flaschen's answer and just wanted to show examples of the options for the case you cannot switch to List (because a library returns you a Collection):

List list = new ArrayList(theCollection);
list.get(5);

Or

Object[] list2 = theCollection.toArray();
doSomethingWith(list[2]);

If you know what generics is I can provide samples for that too.

Edit: It's another question what the intent and semantics of the original collection is.