Swing/ComboBoxOverflowToolTips のバックアップ(No.1)

private static <E> JComboBox<E> makeComboBox(ComboBoxModel<E> model) {
  return new JComboBox<E>(model) {
    @Override public void updateUI() {
      setRenderer(null);
      super.updateUI();
      ListCellRenderer<? super E> renderer = getRenderer();
      JComboBox<E> combo = this;
      JButton arrowButton = getArrowButton(this);
      setRenderer((list, value, index, isSelected, cellHasFocus) -> {
        Component r = renderer.getListCellRendererComponent(
            list, value, index, isSelected, cellHasFocus);
        JComponent c = (JComponent) r;
        // Insets i1 = combo.getInsets();
        Insets ins = c.getInsets();
        // int availableWidth = combo.getWidth() - i1.top - i1.bottom - ins.top - ins.bottom;
        Rectangle rect = SwingUtilities.calculateInnerArea(combo, null);
        // System.out.println(rect);
        int availableWidth = rect.width - ins.top - ins.bottom;

        String str = Objects.toString(value, "");
        FontMetrics fm = c.getFontMetrics(c.getFont());
        c.setToolTipText(fm.stringWidth(str) > availableWidth ? str : null);

        if (index < 0) {
          // @see BasicComboBoxUI#rectangleForCurrentValue
          // System.out.println(UIManager.getBoolean("ComboBox.squareButton"));
          // int buttonSize = combo.getHeight() - i1.top - i1.bottom; // - ins.top - ins.bottom;
          int buttonSize = Objects.nonNull(arrowButton) ? arrowButton.getWidth() : rect.height;
          availableWidth -= buttonSize;
          JTextField tf = (JTextField) combo.getEditor().getEditorComponent();
          availableWidth -= tf.getMargin().left + tf.getMargin().right;
          combo.setToolTipText(fm.stringWidth(str) > availableWidth ? str : null);
        }
        return c;
      });
    }

    private JButton getArrowButton(Container combo) {
      for (Component c: combo.getComponents()) {
        if (c instanceof JButton) {
          return (JButton) c;
        }
      }
      return null;
    }
  };
}