The method sort(List<T>, Comparator<? super T>) in the type Collections is not applicable for the arguments (List<InterfaceMessage>, Folder.CustomComparator)

@Override
public void sortByDate(boolean ascending) {
    Collections.sort(messageList, new CustomComparator());
}

class CustomComparator implements Comparator<Message> {
    public int compare(Message message1, Message message2) {
        return message1.getDate().compareTo(message2.getDate());
    }
}