單例模式 最簡單

class danli{
   protected  $rand;
   protected static $ins = null;
   protected  function  __construct(){
     $this->rand = mt_rand('1','9');
   }
   
   public static function  getins(){
     if(self::$ins == null){
        self::$ins = new self();
     }
     return self::$ins;
   }
}

$a = danli::getins();var_dump($a);
$b = danli::getins();var_dump($b);

 class danli{
            public $db;
            protected static $ins=null;
                protected function __construct(){ 
                    
                    $servername = "localhost";
                    $username = "root";
                    $password = "111111";
                    try {
                        $this->db = new PDO("mysql:host=$servername;dbname=kuaijiezhou", $username, $password);
                        $this->db->exec("SET NAMES 'utf8';");    
                        //echo "Connected successfully"; 
                    }
                    catch(PDOException $e)
                    {
                        echo $e->getMessage();
                    }
               }

                public static  function getins(){
                    if(self::$ins ==null){
                       self::$ins = new self();
                    }
                    return self::$ins;
                }

         }
        $conn = danli::getins()->db;