@Override
  public final int hashCode(){
    int hashCode = 0;
    if (first != null){
      hashCode += hashCode(first);
    }
    if (second != null){
      hashCode += hashCode(second);
    }
    if (third != null){
      hashCode += hashCode(third);
    }
    return hashCode;
  }
@Override
  public final int hashCode()