"+1.+2.+3.4",
            "1.2.3.4e0",
            "6:5:4:3:2:1:0", // too few parts
            "::7:6:5:4:3:2:1:0", // too many parts
            "7:6:5:4:3:2:1:0::", // too many parts
            "9:8:7:6:5:4:3::2:1", // too many parts
            "0:1:2:3::4:5:6:7", // :: must remove at least one 0.
            "3ffe:0:0:0:0:0:0:0:1", // too many parts (9 instead of 8)
            "3ffe::10000", // hextet exceeds 16 bits

    if (IPV4_DELIMITER_MATCHER.countIn(ipString) + 1 != IPV4_PART_COUNT) {
      return null; // Wrong number of parts
    }

    byte[] bytes = new byte[IPV4_PART_COUNT];
    int start = 0;
    // Iterate through the parts of the ip string.
    // Invariant: start is always the beginning of an octet.
    for (int i = 0; i < IPV4_PART_COUNT; i++) {

    if (IPV4_DELIMITER_MATCHER.countIn(ipString) + 1 != IPV4_PART_COUNT) {
      return null; // Wrong number of parts
    }

    byte[] bytes = new byte[IPV4_PART_COUNT];
    int start = 0;
    // Iterate through the parts of the ip string.
    // Invariant: start is always the beginning of an octet.
    for (int i = 0; i < IPV4_PART_COUNT; i++) {

    while (head != null) {
      Listener tmp = head;
      head = head.next;
      tmp.next = reversedList;
      reversedList = tmp;
    }
    return reversedList;
  }

  // TODO(user): move parts into a default method on ListenableFuture?
  @Override
  public String toString() {
    // TODO(cpovirk): Presize to something plausible?
    StringBuilder builder = new StringBuilder();

    while (head != null) {
      Listener tmp = head;
      head = head.next;
      tmp.next = reversedList;
      reversedList = tmp;
    }
    return reversedList;
  }

  // TODO(user): move parts into a default method on ListenableFuture?
  @Override
  public String toString() {
    // TODO(cpovirk): Presize to something plausible?
    StringBuilder builder = new StringBuilder();