class Conexion {
    private static $_dbUser = 'root';
    private static $_dbPass = 'xasasesa';
    private static $_dbDB = 'cobranzas';
    private static $_dbHost = 'localhost';
    private static $_connection = NULL;

    public static function getConnection() {
        if (!self::$_connection) { //evaluo si la conexion no esta establecida ------ self::$_connection / $this->_connection
         self::$_connection = @new mysqli(self::$_dbHost, self::$_dbUser, self::$_dbPass, self::$_dbDB); //establezco la conexion
             if (self::$_connection -> connect_error) {
                die('Connect Error: ' . self::$_connection->connect_error); //Salgo de la ejecución del programa si no logro establecer la conexion
             }
          }
        return self::$_connection; //
    }