MouseWheelで画像のズームイン・アウト表示

class ZoomImage extends JPanel {
  private transient MouseWheelListener handler;
  private final transient Image image;
  private final int iw;
  private final int ih;
  private double scale = 1d;
  protected ZoomImage(Image image) {
    super();
    this.image = image;
    iw = image.getWidth(this);
    ih = image.getHeight(this);
  }

  @Override public void updateUI() {
    removeMouseWheelListener(handler);
    super.updateUI();
    handler = e -> changeScale(e.getWheelRotation());
    addMouseWheelListener(handler);
  }

  @Override protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g.create();
    g2.scale(scale, scale);
    g2.drawImage(image, 0, 0, iw, ih, this);
    g2.dispose();
  }

  public void initScale() {
    scale = 1d;
    repaint();
  }

  public void changeScale(int iv) {
    scale = Math.max(.05, Math.min(5d, scale - iv * .05));
    repaint();
  }
}