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();