静态方法与静态实例

Question

Consider the following code below, I've been thought by Lynda.com to create a database class like this, my question is why not create a static method for the database entirely instead of storing an instance into a static property?

<?php
class Database {

  private $conn;
  private static $init;

  public function __construct() {
     $this->conn = new mysqli('localhost','root','root','mydb');
  }

  public static function getInstance() {
     self::$init = new self();
     return self::$init;
  }

}

$db = Database::getInstance();

?>

Answer 1

If you want to use singleton you should to protect __construct()

class DB
{
  private static $instance;

  private function __construct($args)
  {
    // do some
  }

  public static function getInstance()
  {
    // get instance
  }
}

$query = 'SELECT etc...';
$stmt = DB::getInstance()->prepare($query);

I use this pattern in DB class. But if you have more than 1 connection you should NOT! use singleton.