一个类中的实例是否可以在另一个类的实例中更改变量？

Question

I have just started with OOP, so these are my very first babysteps!

I am trying to build a simple booking system where a user can book a time slot that has been created by another user via a calendar. I am at a very early stage of the project, so the database hasn’t been set up yet and I’m currently fiddling around with a day class and a time slot class and trying to figure out how to make them interact.

Here’s my code:

class dayCL {
    public $dayInMonth;
    public $numBookingSlotsOnDay;

    public function __construct($dayInMonth) {
        $this->dayInMonth = $dayInMonth;
    }
    public function getNumBookingSlotsOnDay(){
        return "Booking slots: " . $this->numBookingSlotsOnDay;
    }
    public function numBookingSlotsOnDay(){
        $this->numBookingSlotsOnDay = $this->numBookingSlotsOnDay + 1 ;
    }
};

class bookingSlotCL {
    public $startTime;

    public function __construct($startTime) {
        $this->startTime = $startTime;
    }
    public function output(){
        return "Start: " . $this->startTime;
    }
};

The numBookingSlotsOnDay function works as intended when called, but is it possible to integrate a call of it in the bookingSlotCL, so it is called on every instantiation of a bookingSlotCL?

Example:

$day1 = new dayCL(1);
$bookingSlot1 = new bookingSlotCL(1);
$bookingSlot2 = new bookingSlotCL(1);

Both booking slots are placed on $day1 so $day1->getNumBookingSlotsOnDay should return “2”.

The calendar is designed so that all days are instantiated as a dayCL instance, which means that a bookingSlotCL instance would always have a dayCL instance to be attached to.

Answer 1

You should add all your bookingSlotCL instances to an array in your dayCL instance like this:

$day1 = new dayCL(1);
$day1->addBooking(new bookingSlotCL());

That addBooking method could look like this:

public function addBooking(dayCL $day) {
    $this->days[] = $day;
    $day->startTime = $this->dayInMonth
}

This way your are even able to change your getNumBookingSlotsOnDay method to dynamically determine the number of booking slots:

public function getNumBookingSlotsOnDay() {
    return count($this->days);
}