@Override
 public void add(User user) {
   String add =
       String.format(
           "insert into Users (name, age) values ('%s', '%d')", user.getName(), user.getAge());
   executor.execUpdate(add);
 }
 @Override
 public void update(User user) {
   String update =
       "update Users set name = "
           + "'"
           + user.getName()
           + "', age = '"
           + user.getAge()
           + "' where id = "
           + "'"
           + user.getId()
           + "'";
   executor.execUpdate(update);
 }