<?php

class Database
{
    protected $db_host = "localhost";
    protected $db_user = "root2"; //здесь специально произведена ошибка. Верное выражение - root в данном случае.
    protected $db_pass = "1111";
    protected $db_name = "program";
    protected $mysqli;


public function connect()
{
  try
  {
    $this->mysqli = new mysqli($this->db_host, $this->db_user, $this->db_pass, $this->db_name);
  }
  catch(Exception $expection)
  {
    echo 'Connection error: ' . $expection->getMessage();
  }
}

}

$database = new Database;
$database->connect();
?>

if ($this->mysqli->connect_errno) {

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);