外部クラスから JPanel の幅と高さを正確に取得する方法は?

public class Rect {
    //... properties

    public void move(JPanel panel) {
        int jpWidth = panel.getWidth();
        int jpHeight = panel.getHeight();

        // rest of the movement logic using jpWidth and jpHeight
    }
}

public void move(Dimension dimension) {
    int jpWidth = dimension.width;
    int jpHeight = dimension.height;

    // rest of the movement logic using jpWidth and jpHeight
}

public class GamePanel extends JPanel implements Runnable {
    
    private Dimension dimension;

    // rest of the class

    public void paint(Graphics g) {
        super.paint(g);

        dimension = new Dimension(getWidth(), getHeight());

        // ...
    }
}

for(Rect rect:rect){
    rect.move(dimension);
}