I'm wondering if there is way to do this without breaking encapsulation, I want the abstract class to rely on parameters defined in the implementing subclass. Like so:

public abstract class Parent {

    private int size;
    private List<String> someList;

    public Parent() {
        size = getSize();
        someList = new ArrayList<String>(size);
    }

    public abstract int getSize();

}

public class Child extends Parent {

    @Override
    public int getSize() {
        return 5;
    }

}

Is this ugly? Is there a better way? And perhaps more importantly, is this even a good idea?