java - 如何从我的 "event"中获取价格因子来计算我的门票价格

Question

我有一个事件类，由 Concert、Play 和 Meeting 实现。我在单独的票类中出售给相应的“事件”。在 Ticket 中，我需要 getPrice() ，它从 10 开始，并且需要在预订事件(具有不同的价格因素)时乘以价格因素。

我试过简单地调用一个静态 PRICE，它是门票的基本价格，并调用了 event.getPriceFactor()，它返回 null，我显然可以在 Ticket 中实例化这个事件。

---

public abstract class Event {
    private String description;
    protected int ticketsSold;
    private int eventId;
    private double priceFactor;
    private static int counter = 1;
    private static final int CAPACITY = 5;
    private ObservableList<Ticket> tickets = 
    FXCollections.observableArrayList();

    /**
     * Stores the description and price factor and assigns a unique id to 
the event.
     * The constructor also allocates the array tickets.
     * 
     * @param description a description of this Play
     * @param priceFactor the price factor for this Play
     * 
     */
    public Event(String description, double priceFactor) {
        this.description = description;
        this.priceFactor = priceFactor;
        this.eventId = computeSerialNumber();
    }

    /**
     * Receives the description and stores that and a price factor of 
1.0. Besides,
     * it assigns a unique id to the event. The constructor also 
allocates the array
     * tickets.
     * 
     * @param description a description of this Play
     * 
     */
    public Event(String description) {
        this(description, 1.0);
    }

    public double getPriceFactor() {
        return priceFactor;
}
------------------------------------------------------------------------------
public class Ticket {

    private static int counter = 1;
    private int serialNumber;
    private double price;
    private static double PRICE = 10.0;
    private Event event;

    /**
     * Creates a ticket for an event. An exception is thrown if there is no space.
     * 
     * @param event the event for which the ticket is being created.
     * @throws NoSpaceException
     */
    public Ticket(Event event) throws NoSpaceException, UnsupportedOperationException { 
            event.addTicket(this);
            this.serialNumber = computeSerialNumber();
    }

    /**
     * Returns the price of the ticket
     * 
     * @return ticket price
     */
    ``public double getPrice() {
        price = Ticket.PRICE * event.getPriceFactor();
        return price;
    }

我期望 Ticket.PRICE (10.) * event.getPriceFactor() (1.0) 返回 10，但它返回 null。

Answer 1

看起来您从未将事件分配给票证构造函数中的票证属性，因此它是一个空值并且无法返回价格因素。尝试分配它，看看是否可行