JLabelの最大幅を共有して異なるパネル間で垂直位置を揃える

// @see javax/swing/plaf/metal/MetalFileChooserUI.java
class AlignedLabel extends JLabel {
  private static final int INDENT = 10;
  // private AlignedLabel[] group;
  protected List<AlignedLabel> group;
  protected int maxWidth;

  protected AlignedLabel(String text) {
    super(text);
    // setAlignmentX(JComponent.LEFT_ALIGNMENT);
    setHorizontalAlignment(SwingConstants.RIGHT);
  }

  @Override public Dimension getPreferredSize() {
    Dimension d = super.getPreferredSize();
    // Align the width with all other labels in group.
    return new Dimension(getMaxWidth() + INDENT, d.height);
  }

  private int getMaxWidth() {
    if (maxWidth == 0 && group != null) {
      int max = group.stream()
        .map(AlignedLabel::getSuperPreferredWidth)
        .reduce(0, Integer::max);
      group.forEach(al -> al.maxWidth = max);
    }
    return maxWidth;
  }

  private int getSuperPreferredWidth() {
    return super.getPreferredSize().width;
  }

  public static void groupLabels(List<AlignedLabel> group) {
    for (AlignedLabel al: group) {
      al.group = group;
    }
  }
}