php pdo connection - singleton

<?php
class DbConn {
    private static $instance;
    private $db;

    private $dbserver;
    private $username;
    private $password;
    private $database;
    private $error;

    public function __construct() {
        $this->dbserver = 'localhost';
        $this->username = 'kick';
        $this->password = '1@kick';
        $this->database = 'kickstartapp';

        try {
            $this->db = new PDO("mysql:host=".$this->dbserver.";dbname=".$this->database, $this->username, $this->password);
        } catch(PDOException $e) {
            $this->error = $e->getMessage();
        }
    }

    public static function getInstance() {
        if(!self::$instance) {
            self::$instance = new self();
        }
        return self::$instance;
    }

    public function getDb() {
        return $this->db;
    }
}


class Database {
    public $db;

    public function __construct() {
        $dbconn = DbConn::getInstance();
        $this->db = $dbconn->getDb();
    }

    public function dbselect($table, $select, $where=NULL) {
    }

    public function dbadd($tablename, $insert, $format) {
    }

    public function dbupdate($tablename, $insert, $where) {
    }
}