Full:

    Matcher m = Pattern.compile("(#\\d+)").matcher(text);
    new StringBuffer buf;    // cool "quicknew" syntax!
    while (m.find())
      m.appendReplacement(buf, m.quoteReplacement(formatSnippetRef(m.group())));
    m.appendTail(buf);
    text = buf.toString();

Short:

    text = text.replaceAll("(#\\d+)", m -> formatSnippetRef(m.group()));