JComboBoxでアイテムが選択されていない場合のプレースホルダ文字列を設定する

JComboBox<String> combo1 = new JComboBox<>(
    new String[] {"One", "Two", "Three", "Four"});
combo1.setSelectedIndex(-1);
combo1.setRenderer(new DefaultListCellRenderer() {
  @Override public Component getListCellRendererComponent(
        JList<?> list, Object value, int index,
        boolean isSelected, boolean cellHasFocus) {
    // ???: String str = index < 0 ? "- Select Item -" : value.toString();
    String str = Objects.toString(value, "- Select Item -");
    super.getListCellRendererComponent(
        list, str, index, isSelected, cellHasFocus);
    return this;
  }
});