static IMeta initMetaOfJComponent(JComponent c) {
  if (c == null) null;
  IMeta meta = cast c.getClientProperty(IMeta);
  if (meta == null)
    c.putClientProperty(IMeta, meta = new Meta);
  ifdef debugComponentMeta
    print("meta of " + c + ": " + meta);
  endifdef
  ret meta;
}