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

Highlighter.HighlightPainter highlightPainter =
    new DefaultHighlighter.DefaultHighlightPainter(Color.YELLOW);
JComboBox<String> combo = new JComboBox<String>(model) {
  @Override public void updateUI() {
    super.updateUI();
    JTextField field = new JTextField(" ");
    field.setOpaque(true);
    field.setBorder(BorderFactory.createEmptyBorder());
    ListCellRenderer<? super String> renderer = getRenderer();
    setRenderer((list, value, index, isSelected, cellHasFocus) -> {
      String pattern = ((JTextField) getEditor().getEditorComponent()).getText();
      if (index >= 0 && !pattern.isEmpty()) {
        Highlighter highlighter = field.getHighlighter();
        highlighter.removeAllHighlights();
        String txt = Objects.toString(value, "");
        field.setText(txt);
        addHighlight(highlighter, Pattern.compile(pattern).matcher(txt));
        field.setBackground(isSelected ? new Color(0xAA_64_AA_FF, true) : Color.WHITE);
        return field;
      }
      return renderer.getListCellRendererComponent(
          list, value, index, isSelected, cellHasFocus);
    });
  }

  private void addHighlight(Highlighter highlighter, Matcher matcher) {
    int pos = 0;
    try {
      while (matcher.find(pos) && !matcher.group().isEmpty()) {
        int start = matcher.start();
        int end = matcher.end();
        highlighter.addHighlight(start, end, highlightPainter);
        pos = end;
      }
    } catch (BadLocationException ex) {
      // should never happen
      RuntimeException wrap = new StringIndexOutOfBoundsException(ex.offsetRequested());
      wrap.initCause(ex);
      throw wrap;
    }
  }
};