Question

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Before you start reading I would like to clarify:

I have already thought of other designs and work arounds
I’m only interested in the problem I exposed and not “changing” it (so no solutions such as delete the points in A and create new points fields in B and C…

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lets consider the following code:

public class A {
    protected cpVect[][] points = null;
    ...
}

and its classes that inherits it:

    public class B extends A{

            ...
    }

    public class C extends A{

            ...
    }

so far so good.

my problem is that for B and C contains arrays of points that will be created in the constructor using something like

if(points == null){calculate points code}

the problem is as follow

points in A can’t be static because the dimensions are different in B and C.

but every instance of B will share the B points and every instance of C will share the C points. (in other words a Square will always be a square and a triangle will always be a triangle). and therefore I want to have the B:points and C:points static so that i don’t get duplicates of the values for every instance.

So is there a way to redefine points as static in B and C when it is not static in A?

Answer 1

If you access points solely through property methods (getters/setters) you can do whatever you want in the subclasses. If you use inheritance, A will have to be an abstract class. Otherwise you’d always carry around the empty points variable in A (losing 8 bytes, probably).

In this case the hierarchy would look like this:

abstract class A {
    abstract public cpVect[][] getPoints();

    // more methods ...
}

public class B extends A {

    private final static cpVect[][] POINTS = calculatePoints();

    @Override
    public cpVect[][] getPoints() {
        return POINTS;
    }

    private cpVect[][] calculatePoints() {
        // ...
    }
}

And the same for C. If A includes no other state or functionality, you should make it an interface.