Question

I need to program a parent class (Plate) and some child classes (WoodenPlate, PorcelainPlate, etc) each of the Child Objects should have a serial number starting with 1, then 2, etc.
Where should I store this information? Can I just increment a counter in the Parent Object?

Answer 1

This is how your one of your Child class should look like:

class WoodenPlate extends Plate {
    private static int counter = 0;
    private int serialNumber;

    public WoodenPlate() {
        serialNumber = ++counter;
    }
}

And then for each instance of WoodenPlate, you can access the serialNumber using public accessors

You can define rest of your Child classes like this. With each one of them having a static counter and a serialNumber field.

---

If you don’t want the count to start from 1 fro every Child, but just want the count to continue from the previous one regardless of which Child class was instantiated, then you should have those fields in Parent class:

class Parent {
    protected static int counter = 0;
    protected int count;

    public int getCount() {
        return count;
    }
}

And then remove the field from each of your Child class.