JComboBoxのEditorComponentにJButtonを配置

class SiteComboBoxLayout implements LayoutManager {
  private final JLabel favicon;
  private final JButton feedButton;

  protected SiteComboBoxLayout(JLabel favicon, JButton feedButton) {
    this.favicon = favicon;
    this.feedButton = feedButton;
  }

  @Override public void addLayoutComponent(String name, Component comp) {
    /* not needed */
  }

  @Override public void removeLayoutComponent(Component comp) {
    /* not needed */
  }

  @Override public Dimension preferredLayoutSize(Container parent) {
    return parent.getPreferredSize();
  }

  @Override public Dimension minimumLayoutSize(Container parent) {
    return parent.getMinimumSize();
  }

  @Override public void layoutContainer(Container parent) {
    if (!(parent instanceof JComboBox)) {
      return;
    }
    JComboBox<?> cb = (JComboBox<?>) parent;
    int width = cb.getWidth();
    int height = cb.getHeight();
    Insets insets = cb.getInsets();
    int arrowHeight = height - insets.top - insets.bottom;
    int arrowWidth = arrowHeight;
    int faviconWidth = arrowHeight;
    int feedWidth; // = arrowHeight;

    // Arrow Icon JButton
    JButton arrowButton = (JButton) cb.getComponent(0);
    if (Objects.nonNull(arrowButton)) {
      Insets arrowInsets = arrowButton.getInsets();
      arrowWidth = arrowButton.getPreferredSize().width
        + arrowInsets.left + arrowInsets.right;
      arrowButton.setBounds(width - insets.right - arrowWidth, insets.top,
                            arrowWidth, arrowHeight);
    }

    // Favicon JLabel
    if (Objects.nonNull(favicon)) {
      Insets faviconInsets = favicon.getInsets();
      faviconWidth = favicon.getPreferredSize().width
          + faviconInsets.left + faviconInsets.right;
      favicon.setBounds(insets.left, insets.top, faviconWidth, arrowHeight);
    }

    // Feed Icon JButton
    if (Objects.nonNull(feedButton) && feedButton.isVisible()) {
      Insets feedInsets = feedButton.getInsets();
      feedWidth = feedButton.getPreferredSize().width
          + feedInsets.left + feedInsets.right;
      feedButton.setBounds(width - insets.right - feedWidth - arrowWidth, insets.top,
                           feedWidth, arrowHeight);
    } else {
      feedWidth = 0;
    }

    // JComboBox Editor
    Component editor = cb.getEditor().getEditorComponent();
    if (Objects.nonNull(editor)) {
      editor.setBounds(insets.left + faviconWidth, insets.top,
          width  - insets.left - insets.right - arrowWidth - faviconWidth - feedWidth,
          height - insets.top  - insets.bottom);
    }
  }
}