@Override
  public boolean equals(Object obj) {
    if (this == obj) return true;
    if (obj == null) return false;
    if (!(obj instanceof User)) return false;
    User other = (User) obj;
    if (firstName == null) {
      if (other.firstName != null) return false;
    }
    else if (!firstName.equals(other.firstName)) return false;
    if (lastName == null) {
      if (other.lastName != null) return false;
    }
    else if (!lastName.equals(other.lastName)) return false;
    return true;
  }