public static function getInstance()
 {
     if (!self::$_instance instanceof self) {
         self::$_instance = new self();
     }
     return self::$_instance;
 }
<?php

/**
* Plugin Name:       uPrint Management Plugin
* Plugin URI:        http://www.tailoredmarketing.co.uk
* Description:       This plugin provides the management functions for the uPrint website
* Version:           1.0.0
* Author:            @DanTaylorSEO
* Author URI:        http://www.tailoredmarketing.co.uk
* License:           GPL-2.0+
* License URI:       http://www.gnu.org/licenses/gpl-2.0.txt
**/
// If this file is called directly, abort.
if (!defined('WPINC')) {
    die;
}
define('PLUGIN_DIR', dirname(__FILE__) . '/');
define('PLUGIN_URL', plugin_dir_url(__FILE__) . '/');
require PLUGIN_DIR . 'classes/uprint-management-plugin.class.php';
uPrintManagementPlugin::getInstance();
register_activation_hook(__FILE__, array('uPrintManagementPlugin', 'plugin_activation'));