public LimitedSkiPass(int id, String type, Date activationDate, Date expirationDate,
            int numPassages) {
        super(id, type, activationDate, expirationDate);
        if (numPassages <= 0) {
            throw new IllegalArgumentException(
                    "Non-positive number of passages is not allowed");
        }
        this.numPassages = numPassages;
    }