FXCollections.observableArrayList nullpointer

Question

希望有人可以帮我解决这个问题。 我尝试为一堂课做一个Junit考试。 但不知何故，当我尝试创建一个要测试的对象时，我总是会收到nullpointer。

我的二年级学生在课堂上出了问题。

private ReservatieSpecificatie geselecteerdeResSpec;
private long id;
private GebruikerRepository gebruikerRepository;
DBCommunicatie databank = new DBCommunicatie();
private SimpleListProperty reservaties = new SimpleListProperty();
private SimpleObjectProperty ophaalMoment = new SimpleObjectProperty();
private SimpleObjectProperty indienMoment = new SimpleObjectProperty<>();
private SimpleStringProperty email = new SimpleStringProperty();

public Reservatie(Calendar ophaalMoment, Calendar indienMoment, List<ReservatieSpecificatie> reservaties, String email) {
    gebruikerRepository = new GebruikerRepository(databank);
    setOphaalMoment(ophaalMoment);
    setIndienMoment(indienMoment);
    setReservaties(reservaties);
    setEmail(email);

}

   public void setReservaties(List<ReservatieSpecificatie> reservaties) {
            this.reservaties.set(FXCollections.observableArrayList(reservaties));
        }

我接受了这个错误的轨道：

java.lang.NullPointerException
    at java.util.AbstractCollection.addAll(AbstractCollection.java:343)
    at javafx.collections.ModifiableObservableListBase.addAll(ModifiableObservableListBase.java:99)
    at javafx.collections.FXCollections.observableArrayList(FXCollections.java:341)
    at domein.Reservatie.setReservaties(Reservatie.java:133)
    at domein.Reservatie.<init>(Reservatie.java:65)
    at domein.ReservatieTest.setUp(ReservatieTest.java:45)

提前感谢。

Answer 1

在AbstractCollection.addAll() NullPointerException中，当＆＃34;指定的集合包含null元素且此集合不允许null元素时，您会看到reservaties被抛出，或者如果指定的集合为null。＆＃34;因此，val()参数本身为null，或者更可能是包含null元素。