JTableでファイルとディレクトリを別々にソート

// > dir /O:GN
// > ls --group-directories-first
class FileGroupComparator extends DefaultFileComparator {
  private static final long serialVersionUID = 1L;
  private final JTable table;
  public FileGroupComparator(JTable table, int column) {
    super(column);
    this.table = table;
  }

  @Override public int compare(File a, File b) {
    int flag = 1;
    List<? extends TableRowSorter.SortKey> keys = table.getRowSorter().getSortKeys();
    if (!keys.isEmpty()) {
      TableRowSorter.SortKey sortKey = keys.get(0);
      if (sortKey.getColumn() == column &&
          sortKey.getSortOrder() == SortOrder.DESCENDING) {
        flag = -1;
      }
    }
    if (a.isDirectory() && !b.isDirectory()) {
      return -1 * flag;
    } else if (!a.isDirectory() && b.isDirectory()) {
      return 1 * flag;
    } else {
      return super.compare(a, b);
    }
  }
}