private <T> List<List<T>> cartesianProduct(List<List<T>> lists) {
        List<List<T>> resultLists = new ArrayList<>();
        if (lists.size() == 0) {
            resultLists.add(new ArrayList<>());
            return resultLists;
        } else {
            List<T> firstList = lists.get(0);
            List<List<T>> remainingLists = cartesianProduct(lists.subList(1, lists.size()));
            for (T condition : firstList) {
                for (List<T> remainingList : remainingLists) {
                    ArrayList<T> resultList = new ArrayList<>();
                    resultList.add(condition);
                    resultList.addAll(remainingList);
                    resultLists.add(resultList);
                }
            }
        }
        return resultLists;
    }
 

說明：先將要計算的笛卡爾積集合一起放到一個大集合中。