添加到链接列表时出现java.lang.stackoverflowerror

尝试将对象添加到链表（java util）时遇到此问题 我有一个Doctor和Patient类，都继承自抽象类Person

public abstract class Person {
    private LinkedList<Appointment> scheduledAppointments = new LinkedList<Appointment>();

    //irrelevant code

    public boolean addAppointment(Appointment appointment){
        return this.scheduledAppointments.add(appointment);
    }

参与者属性在链接列表中具有医生和患者。

public class Appointment {
    private ArrayList<Person> participants = new ArrayList<Person>();
    ...

    public Appointment(Person doctor, Person patient, int day, int month, int year, double startHour, Procedure procedure) {
        this.participants.add(doctor);
        this.participants.add(patient);
        ...
        }

    public void addAppointmentToParticipants(){
        for (Person person : participants) {
            person.addAppointment(this);
        }
    }

the problem occurs when i'm trying to add the Appointment to each of the participants: Method threw 'java.lang.StackOverflowError' exception. Cannot evaluate Appointment.toString()

当我调试它时，我可以看到该异常发生在LinkedList.java上， 特别是在size ++行上

   void linkLast(E e) {
        final Node<E> l = last;
        final Node<E> newNode = new Node<>(l, e, null);
        last = newNode;
        if (l == null)
            first = newNode;
        else
            l.next = newNode;
        size++;
        modCount++;
    }

我不明白为什么我会遇到这个问题，“ toString”与它有什么关系...