@Override
    public int hashCode() {
        int result = stock != null ? stock.hashCode() : 0;
        result = 31 * result + (int) (price ^ (price >>> 32));
        result = 31 * result + (seller != null ? seller.hashCode() : 0);
        result = 31 * result + (buyer != null ? buyer.hashCode() : 0);
        result = 31 * result + (tradeDate != null ? tradeDate.hashCode() : 0);
        return result;
    }