Java abstract class constants

Question

I have the following abstract class:

public abstract class GameObject {
protected final GameSession session;
protected final int id;
protected Point position;

public GameObject(GameSession session, Point position) {
    this.position = position;
    this.id = session.getNewId();
    this.session = session;
}

public void setPosition(Point position) {
    this.position = position;
}

public int getId() {
    return id;
}

public Point getPosition() {
    return position;
}

Each gameObject also contains constants WIDTH and HEIGHT . I want to add method getBar() for all game objects which supposed to use these constants. Here an example of game object:

public class Wall extends GameObject {
private static final Logger logger = LogManager.getLogger(Wall.class);
private static final int WIDTH = 32;
private static final int HEIGHT = 32;

public Wall(GameSession session, Point position) {
    super(session, position);
    logger.info("New Wall id={}, position={}", id, position);
}

And getbar() if it were in Wall class:

public Bar getBar() {
    return new Bar(position, position.getX() + WIDTH, position.getY() + HEIGHT);
}

How should I implement GameObject correctly? The problem is that i can't just initialize WIDTH and HEIGHT inside because they are different in subclasses.

Answer 1

Define abstract method getBar() in your abstract class GameObject

public abstract Bar getBar()

Then all classes which extends GameObject must implement them. So for example Wall class will have method

@Override
public Bar getBar() {
    return new Bar(position, position.getX() + WIDTH, position.getY() + HEIGHT);
}

Alternatively you can create constructor in GameObject which will also takes these constants and then you can have single method call (no need to override it):

public abstract class GameObject {
    protected final GameSession session;
    protected final int id;
    protected Point position;
    protected final width;
    protected final height;

public GameObject(GameSession session, Point position, int width, int height) {
    this.position = position;
    this.id = session.getNewId();
    this.session = session;
    this.width = width;
    this.height = height;
}

    public Bar getBar() {
        return new Bar(position, position.getX() + width, position.getY() + height);
    }
}

then in your Wall class

public Wall(GameSession session, Point position) {
    super(session, position, 32, 32); //Added WIDTH and HEIGHT
    logger.info("New Wall id={}, position={}", id, position);
}