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

class AlternateRowColorTree extends JTree {
  private static final Color SELECTED_COLOR = new Color(0x64_32_64_FF, true);

  @Override protected void paintComponent(Graphics g) {
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setPaint(new Color(0xCC_CC_CC));
    IntStream.range(0, getRowCount())
        .filter(i -> i % 2 == 0)
        .mapToObj(this::getRowBounds)
        .forEach(r -> g2.fillRect(0, r.y, getWidth(), r.height));

    int[] selections = getSelectionRows();
    if (selections != null) {
      g2.setPaint(SELECTED_COLOR);
      Arrays.stream(selections)
          .mapToObj(this::getRowBounds)
          .forEach(r -> g2.fillRect(0, r.y, getWidth(), r.height));
      super.paintComponent(g);
      if (hasFocus()) {
        Optional.ofNullable(getLeadSelectionPath()).ifPresent(path -> {
          Rectangle r = getRowBounds(getRowForPath(path));
          g2.setPaint(SELECTED_COLOR.darker());
          g2.drawRect(0, r.y, getWidth() - 1, r.height - 1);
        });
      }
    }
    super.paintComponent(g);
    g2.dispose();
  }

  @Override public void updateUI() {
    super.updateUI();
    UIManager.put("Tree.repaintWholeRow", Boolean.TRUE);
    setCellRenderer(new TransparentTreeCellRenderer());
    setOpaque(false);
  }
}