探讨PHP 静态变量 静态方法 初始化类的问题 哪种写法合格

class Main {

static $service;

public function __construct() {
$this->getService ()->t ();
$this->getService ()->t ();

}

public static function getService1() {

return new Service ( "BB" );

}

public static function getService2() {
if (self::$service == null) {
self::$service = new Service ();
}
return self::$service;
}

public function getService3() {

return self::$service = new Service ( "BB" );

}
}
//请问service类初始化了几次  那种getservice写法合格
new Main ();