How to classify the same field values in a list under the same list

Method 1  

List<List<User>> result = new ArrayList<>();
Map<Integer,List<User>> map = new HashMap<>();
//userList To operate list aggregate
for (User user : userList) {
    Integer age = user.getAge();
    List<User > lstUser;
    if (map.containsKey(age)) {
        lstUser= map.get(age);
    }else{
        lstUser= new ArrayList<>();
    }
    lstUser.add(user);
    map.put(age,lstUser);
}
for (Map.Entry<Integer, List<User>> entry : map.entrySet()) {
    result.add(entry.getValue());
}

Method 2

List<List<AirTimeRangeContract>> result = new ArrayList<List<AirTimeRangeContract>>();
        Map<Long, List<AirTimeRangeContract>> map = new TreeMap<Long, List<AirTimeRangeContract>>();

        for (AirTimeRangeCon