A Queue that ensure uniqueness of the elements?

Question

I\'m looking for a implementation of java.util.Queue or something in the Google collection who behave like a Queue, but also ensure that each element of the queue is unique.

Answer 1

How about a LinkedHashSet? Its iterator preserves insertion order, but because it's a Set, its elements are unique.

As its documentation says,

Note that insertion order is not affected if an element is re-inserted into the set.

In order to efficiently remove elements from the head of this "queue", go through its iterator:

Iterator i = queue.iterator();
...
Object next = i.next();
i.remove();