@Override
  public boolean equals(Object obj)
  {
    if (this == obj) {
      return true;
    }
    if (obj == null) {
      return false;
    }
    if (getClass() != obj.getClass()) {
      return false;
    }
    Edge other = (Edge) obj;
    if (end == null) {
      if (other.end != null) {
        return false;
      }
    } else if (!end.equals(other.end)) {
      return false;
    }
    if (start == null) {
      if (other.start != null) {
        return false;
      }
    } else if (!start.equals(other.start)) {
      return false;
    }
    return true;
  }