java - 按日期和时间对 ArrayList 的对象进行排序

Question

我在 ArrayList 中有 10 个对象，其中患者 ID 和预约日期作为实例变量。如何按预约日期对患者进行排序？

出于某种原因，我无法使用Comparator 对ArrayList 进行排序；编译器报错:

java.util.Comparator is abstract; cannot be instantiated

Collections.sort() 在不使用 Comparator 时对 Object 不起作用。

ArrayList<Appointment> testApp = new ArrayList<>();

while (!App.isEmpty()) {
    tempA = (Appointment) App.dequeue();

    if (tempA.getPatID().equals(search)) {
        testApp.add(tempA);
    }

    tempApp.enqueue(tempA);
}

while (!tempApp.isEmpty()) {
    tempA = (Appointment) tempApp.dequeue();
    App.enqueue(tempA);
}

Collections.sort(testApp, new Comparator<Appointment>());

Answer 1

我假设您的 Appointment 类看起来像这样:

class Appointment {
    private int patientId;
    private LocalDateTime appointmentDate;

    // Getters & setters
}

如果是这样，您将创建一个 Comparator 以使用 Comparator.comparing 进行排序方法:

ArrayList<Appointment> appointments = new ArrayList<>();

Collections.sort(appointments, Comparator.comparing(appointment -> {
    return appointment.getAppointmentDate();
}));

该 lambda 函数告诉比较器如何获取您的对象(Appointment)并提取用于排序的元素(键；appointmentDate)。如果您愿意，可以将其压缩为方法引用:

Collections.sort(appointments, Comparator.comparing(Appointment::getAppointmentDate));

您也可以调用Collection#sort()直接在 ArrayList 上:

appointments.sort(Comparator.comparing(Appointment::getAppointmentDate));

---

如果您总是(或通常)按日期对Appointment 对象进行排序，您可以考虑让Appointment 实现Comparable这样您就可以在不传递 Comparator 的情况下调用 .sort():

class Appointment implements Comparable<Appointment> {
    private int patientId;
    private LocalDateTime appointmentDate;

    // Getters & setters

    @Override
    public int compareTo(final Appointment other) {
        return appointmentDate.compareTo(other.appointmentDate);
    }
}