JTableで同一内容のセルを空表示にしてグループ化を表現する

String colors = "colors";
String sports = "sports";
String food = "food";
addRowData(model, new RowData(colors, "blue", 1));
addRowData(model, new RowData(colors, "violet", 2));
addRowData(model, new RowData(colors, "red", 3));
addRowData(model, new RowData(colors, "yellow", 4));
addRowData(model, new RowData(sports, "baseball", 23));
addRowData(model, new RowData(sports, "soccer", 22));
addRowData(model, new RowData(sports, "football", 21));
addRowData(model, new RowData(sports, "hockey", 20));
addRowData(model, new RowData(food, "hot dogs", 10));
addRowData(model, new RowData(food, "pizza", 11));
addRowData(model, new RowData(food, "ravioli", 12));
addRowData(model, new RowData(food, "bananas", 13));
// ...
class RowDataRenderer implements TableCellRenderer {
  private final TableCellRenderer renderer = new DefaultTableCellRenderer();
  @Override public Component getTableCellRendererComponent(
      JTable table, Object value, boolean isSelected, boolean hasFocus,
      int row, int column) {
    JLabel label = (JLabel) renderer.getTableCellRendererComponent(
        table, value, isSelected, hasFocus, row, column);
    label.setHorizontalAlignment(SwingConstants.LEFT);
    RowData data = (RowData) value;
    switch (table.convertColumnIndexToModel(column)) {
    case 0:
      String str = data.getGroup();
      if (row > 0) {
        RowData prev = (RowData) table.getValueAt(row - 1, column);
        if (Objects.equals(prev.getGroup(), str)) {
          label.setText(" ");
          break;
        }
      }
      label.setText("+ " + str);
      break;
    case 1:
      label.setText(data.getName());
      break;
    case 2:
      label.setHorizontalAlignment(SwingConstants.RIGHT);
      label.setText(Integer.toString(data.getCount()));
      break;
    default:
      break;
    }
    return label;
  }
}