class StringUtils {
    public static String join(List<String> list, String separator) {<FILL_FUNCTION_BODY>}
}

        StringBuilder sb = new StringBuilder();
        boolean first = true;
        for (String item : list) {
            if (first) first = false;
            else sb.append(separator);

            sb.append(item);
        }
        return sb.toString();
    
<no_super_class>