observer_list)) {            $this->observer_list[] = $observer;        }    }    // 向观察者发送消息,告诉它主题有改变    public function notify()    {        if(!empty($this->observer_list)) {            foreach($this->observer_list as $ob) {                $ob->update();            }        }    }}$ob1 = new Observer1();$ob2 = new Observer2();$subj = new Subject();// 注册观察者$subj->reg_observer($ob1);$subj->reg_observer($ob2);// 向观察者推送消息$subj->notify();