public static int update(User user) {
        ConnectionPool pool = ConnectionPool.getInstance();
        Connection connection = pool.getConnection();
        PreparedStatement ps = null;

        String query = "UPDATE user SET username = ?, password = ?, email = ?, firstName = ?, lastName = ?"
                + "WHERE userID = ?";

        try {
            ps = connection.prepareStatement(query);
            ps.setString(1, user.getUsername());
            ps.setString(2, user.getPassword());
            ps.setString(3, user.getEmail());
            ps.setString(4, user.getFirstName());
            ps.setString(5, user.getLastName());
            ps.setInt(6, user.getUserID());
            return ps.executeUpdate();
        } catch (SQLException e) {
            System.out.println(e);
        } finally {
            DBUtil.closePreparedStatement(ps);
            pool.freeConnection(connection);
        }
        return 0;
    }