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

class ColumnWidthResizeHandler extends MouseInputAdapter {
  private final JWindow window = new JWindow();
  private final JToolTip tip = new JToolTip();
  private String prev = "";

  private Point getToolTipLocation(MouseEvent e) {
    Point p = e.getPoint();
    Component c = e.getComponent();
    SwingUtilities.convertPointToScreen(p, c);
    p.translate(0, -tip.getPreferredSize().height);
    return p;
  }

  private static TableColumn getResizingColumn(MouseEvent e) {
    Component c = e.getComponent();
    if (c instanceof JTableHeader) {
      return ((JTableHeader) c).getResizingColumn();
    }
    return null;
  }

  private void updateTooltipText(MouseEvent e) {
    TableColumn column = getResizingColumn(e);
    if (column != null) {
      String txt = String.format("Width: %dpx", column.getWidth());
      tip.setTipText(txt);
      if (prev.length() != txt.length()) {
        window.pack();
      }
      window.setLocation(getToolTipLocation(e));
      prev = txt;
    }
  }

  @Override public void mouseDragged(MouseEvent e) {
    if (!window.isVisible() && getResizingColumn(e) != null) {
      window.add(tip);
      window.setAlwaysOnTop(true);
      window.setVisible(true);
    }
    updateTooltipText(e);
  }

  @Override public void mouseReleased(MouseEvent e) {
    window.setVisible(false);
  }
}