sclass JNavigation extends JPanel {
  JList list;
  SingleComponentPanel content;
  new Map<S, F0<JComponent>> contentMakers;
  S lastItem;

  *() {
    makeFakeSingleComponentPanel(this, jhsplit(list, content));
    onChange(list, r {
      S item = getSelectedItem(list);
      if (eq(item, lastItem)) ret;
      lastItem = item;
      JComponent content = pcallF(contentMakers.get(item));
      if (content == null) content = jcenteredimage(#1101244);
      scp.setComponent(content);
    }
  }
  
  void addPage(fS name, final F0<JComponent> makeContent) {
    swing {
      contentMakers.put(name, makeContent);
      addListItem(list, name);
    }
  }
}