Database Class - Pagination

<?php

class Database
{
    private $conn;
    private static $instance = null;

    private $host = 'localhost';
    private $db = 'test_db';
    private $username = 'test';
    private $password = 'test';

    public static function getInstance()
    {
        if (is_null(static::$instance)) {
            static::$instance = new static;
        }

        return static::$instance;
    }

    private function __construct()
    {
        try {
            $this->conn = new PDO('mysql:host=' . $this->host . ';dbname=' . $this->db, $this->username, $this->password);
            $this->conn->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_OBJ);
        } catch (\PDOException $e) {
            die('Unable to connect to database:' . $e->getMessage());
        }
    }

    private function __clone() {}

    private function __wakeup() {}

    public function getConnection()
    {
        return $this->conn;
    }
}