没理解本节支付接口的 设置用意,他与支付二维码功能不同在哪

public void pay(String orderNo){
    Order order = orderMapper.selectByOrderNo(orderNo);
    //查不到订单,报错
    if (order == null) {
throw new ImoocMallException(ImoocMallExceptionEnum.NO_ORDER);

    }
if(order.getOrderStatus()== Constant.OrderStatusEnum.NOT_PAID.getCode()){
        order.setOrderStatus(Constant.OrderStatusEnum.PAID.getCode());

        orderMapper.updateByPrimaryKeySelective(order);
    }else{
throw new ImoocMallException(ImoocMallExceptionEnum.WRONG_ORDER_STATUS);
    }