php单例设计模式

class car {
static $obj = null;
private function __construct(){}
static function getObj(){
if(is_null(self::$obj)){
self::$obj = new car;
}
return self::$obj;
}
function __destruct(){
echo "********************<br>";
}
function say(){
echo 'Hello World!<br>';
}
}$c = car::getObj();
$d = car::getObj();
$e = car::getObj();
$f = car::getObj();
$c = car::getObj();
$c->say();
$f->say();