java - Is there an insertion order preserving Set that also implements List?

Question

I'm trying to find an implementation of java.util.List and java.util.Set at the same time in Java. I want this class to allow only unique elements (as Set) and preserve their order (like List). Does it exist in JDK 6?

It's important to have List<T>#add(int, T) so I can insert into a specific position.

Answer 1

TreeSet is sorted by element order; LinkedHashSet retains insertion order. Hopefully one of those is what you were after.

You've specified that you want to be able to insert at an arbitrary location, I suspect you'll have to write your own - just create a class containing a HashSet<T> and an ArrayList<T>; when adding an item, check whether or not it's in the set before adding it to the list.

Alternatively Apache's commons-collections4 offers ListOrderedSet and SetUniqueList, which behave similarly and should meet the given requirements.