Unused variables from superclass

Question

class ABC {
    private int[] variable;
    public int[] getVariable() {
        return variable;
    }
    public ABC() {
        variable = new int[123456];
    }
}

class DEF extends ABC {
    public int[] getVariable() {
        return new int[0];
    }
} 

variable is used in ABC, but completely unused and needless in DEF. But I can't see any proper way to prevent creating this big array in DEF, because always some constructor of superclass has to be executed. I see only one, inelegant way: new, "fake" constructor for ABC:

protected ABC(boolean whatever) {}

Then in DEF I can write:

public DEF() {
    super(true);
}

and it works - variable isn't initialized.

But, my question is - can I solve this more properly?

Maybe if variable is unused, compiler automatically deletes her? It's quite often situation, when such feature could be useful.

Answer 1

Are you sure DEF needs to extend ABC - I mean, is a DEF logically a ABC? Inheritance is powerful but needs to be used with caution.

In your case, I'd rather have:

public interface WithVariable {
  int[] getVariable();
}

And have both ABC and DEF implementing WithVariable. This way constructing a ABC object will initialise the needed variable, and constructing a DEF object won't do anything, but they'll both reply to the same message (getVariable()).