Swing/RoundedCornerListCellRenderer のバックアップ(No.1)

class RoundedCornerListCellRenderer<E> implements ListCellRenderer<E> {
  private static final Icon GAP = new GapIcon();
  private final DefaultListCellRenderer renderer = new DefaultListCellRenderer() {
    @Override protected void paintComponent(Graphics g) {
      if (getIcon() != null) {
        Graphics2D g2 = (Graphics2D) g.create();
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setPaint(getBackground());
        Rectangle r = SwingUtilities.calculateInnerArea(this, null);
        g2.fill(new RoundRectangle2D.Float(r.x, r.y, r.width, r.height, 10f, 10f));
        super.paintComponent(g2);
        g2.dispose();
      } else {
        super.paintComponent(g);
      }
    }
  };

  @Override public Component getListCellRendererComponent(JList<? extends E> list, E value, int index, boolean isSelected, boolean cellHasFocus) {
    Component c = renderer.getListCellRendererComponent(
        list, value, index, isSelected, cellHasFocus);
    if (c instanceof JLabel) {
      JLabel label = (JLabel) c;
      label.setOpaque(false);
      label.setBorder(BorderFactory.createEmptyBorder(2, 2, 2, 2));
      label.setIconTextGap(0);
      label.setIcon(index >= 0 ? GAP : null);
      // Nimbus DerivedColor bug?
      Color fgc = isSelected
          ? new Color(list.getSelectionForeground().getRGB())
          : list.getForeground();
      label.setForeground(fgc);
    }
    return c;
  }
}

class GapIcon implements Icon {
  @Override public void paintIcon(Component c, Graphics g, int x, int y) {
    /* Empty paint */
  }

  @Override public int getIconWidth() {
    return 2;
  }

  @Override public int getIconHeight() {
    return 18;
  }
}