String (Couple<List<Integer>> pairs) { StringBuilder result = new StringBuilder(); List<Integer> codes = pairs.getFirst(); List<Integer> modifiers = pairs.getSecond(); for (int i = 0; i < codes.size(); i++) { Integer each = codes.get(i); result.append(each.toString()); result.append(MODIFIER_DELIMITER); result.append(modifiers.get(i)); if (i < codes.size() - 1) { result.append(CODE_DELIMITER); } } return result.toString(); }