java如何从我的“活动”中获取价格因子来计算我的门票价格

Question

我有一个活动课程，通过音乐会、戏剧和会议来实施。我在一个单独的票舱里，为一个单独的“活动”出售在Ticket中，我需要获取price（），它从10开始，在预订活动（具有不同的价格因素）时需要乘以价格因素

我试着简单地调用一个静态价格，这是一张票的基本价格，并调用事件。getPriceFactor（）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;
    }

我在等票。价格（10）*事件getPriceFactor（）（1.0）返回10，但返回null