Is there a way to create a List/Set which keeps insertion order and does not allow duplicates in Java?

Question

What is the most efficient way of maintaining a list that does not allow duplicates, but maintains insertion order and also allows the retrieval of the last inserted element in Java?

Answer 1

Try LinkedHashSet, which keeps the order of input.

Note that re-inserting an element would update its position in the input order, thus you might first try and check whether the element is already contained in the set.

Edit:

You could also try the Apache commons collections class ListOrderedSet which according to the JavaDoc (if I didn't missread anything again :) ) would decorate a set in order to keep insertion order and provides a get(index) method.

Thus, it seems you can get what you want by using new ListOrderedSet(new HashSet());

Unfortunately this class doesn't provide a generic parameter, but it might get you started.

Edit 2:

Here's a project that seems to represent commons collections with generics, i.e. it has a ListOrderedSet<E> and thus you could for example call new ListOrderedSet<String>(new HashSet<String>());