code: public static String insert(final String str, final String c, final int pos) {
      if (str.length() < pos) { return str; }
      return str.substring(0, pos - 1) + c + str.substring(pos);
    }
docs: <p>
  insert.
  </p>
  
  @param str a {@link java.lang.String} object.
  @param c a {@link java.lang.String} object.
  @param pos a int.
  @return a {@link java.lang.String} object.