In multiple `HashSet` of `Integers` I want to get all those elements, which has no duplicate. i.e. which came only once in union of all the `HashSet`. I am not able to conceptualize it programmatically.  

 As an example, consider set first contains {2,4,6,8,9}, second set contains {2,8,9} and third set contains {2,4,8,9}. In all these set, element 6 occurs only once.  

How to find all the elements which has no duplicate in multiple HashSet of Integers in Java?