Hash Set and Array List performances

Question

I have implemented a method which simply loops around a set of CSV files that contain data on a number of different module. This then adds the \'moduleName\' into a hashSet.

Answer 1

They're completely different classes, so the question is: what kind of behaviour do you want?

HashSet ensures there are no duplicates, gives you an O(1) contains() method but doesn't preserve order.
ArrayList doesn't ensure there are no duplicates, contains() is O(n) but you can control the order of the entries.