HashSet is the implementation of Set interface , It uses HashMap internally for holding the elements. HashMap stores all the elements as a key value pair but , in HashSet we have only one thing i.e values , so in HashMap we store all the values as key with same values for all the data.
Private Map map; Object sameValueObject = new Object(); Public void add(Object element) { Map.put(same); }
Because HashMap keys are unique , so it guarantees for uniqueness.