[Lógica] Posição do mouse - o tamanho do desenho

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Rectangle2D;

import javax.swing.JFrame;

public class Janela extends JFrame {
    private Rectangle2D.Double quad = new Rectangle2D.Double(50, 50, 50, 50);

    public static void main(String[] args) {
        new Janela().setVisible(true);
    }

    public Janela() {
        setSize(250, 250);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        MouseHandler handler = new MouseHandler();
        addMouseMotionListener(handler);
        addMouseListener(handler);
        setBackground(Color.GRAY);
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        Graphics2D g2d = (Graphics2D) g.create();
        g2d.setColor(Color.RED);
        g2d.draw(quad);
        g2d.dispose();
    }

    public class MouseHandler extends MouseAdapter {
        private boolean mouseDownOnQuad = false;
        @Override
        public void mousePressed(MouseEvent e) {
            mouseDownOnQuad = quad.contains(e.getPoint());
        }

        @Override
        public void mouseReleased(MouseEvent e) {
            mouseDownOnQuad = false;
        }
        
        @Override
        public void mouseDragged(MouseEvent e) {            
            if (!mouseDownOnQuad)
                return;
            quad.x = e.getX() - (quad.width / 2.0);
            quad.y = e.getY() - (quad.height / 2.0);
            repaint();
        }
    }
}