private static Set difFiles(String[] files1, String[] files2) {
    Set set1 = new HashSet();
    Set set2 = new HashSet();
    Set extra = new HashSet();
    for (int x=0; x < files1.length; x++) {
      set1.add(files1[x]);
    }
    for (int x=0; x < files2.length; x++) {
      set2.add(files2[x]);
    }
    Iterator i1 = set1.iterator();
    while (i1.hasNext()) {
      Object o = i1.next();
      if (!set2.contains(o)) {
        extra.add(o);
      }
    }
    Iterator i2 = set2.iterator();
    while (i2.hasNext()) {
      Object o = i2.next();
      if (!set1.contains(o)) {
        extra.add(o);
      }
    }
    return extra;
  }