public class FindDups2 {
  public static void main(String[] args) {
    Set<String> uniques = new HashSet<String>();
    Set<String> dups    = new HashSet<String>();

    for (String a : args)
      if (!uniques.add(a))
        dups.add(a);

    // Destructive set-difference
    uniques.removeAll(dups);

    System.out.println("Unique words:    " + uniques);
    System.out.println("Duplicate words: " + dups);
  }
}