static int latestInstalledJavaX() {
  File[] files = new File(userHome(), ".javax").listFiles();
  int v = 0;
  if (files != null) for (File f : files) {
    Matcher m = regexpMatcher("x(\\d\\d\\d?)\\.jar", f.getName());
    if (m.matches())
      v = Math.max(v, Integer.parseInt(m.group(1)));
  }
  return v;
}