java - 如何获取 Observablelist 中的所有唯一属性并统计唯一属性？

Question

我有一个ObservalbeList<Appointment> appointments 。每个appointment有一个type属性是一个字符串，可以返回 type与 getType()方法。理想情况下，如果约会列表包含“常规、审核、每周、每周”，则输出将是:

General: 1, 
Review: 1,  
Weekly: 2

虽然我可以迭代列表，但我在跟踪唯一值和这些值的计数时遇到了困难。

有推荐的方法可以实现这个吗？以下是我目前拥有的。

    public void clickMenuReportsItemNumberOfAppointmentsByType(ActionEvent event) throws IOException{

        TextAreaOutput.clear();

        AppointmentDOA appointmentDOA = new AppointmentDOA(DBConnection.getConnection());
        ObservableList<Appointment> Appointments = appointmentDOA.findAll();

        // get all the types
        // check the number of times each type shows up
        ObservableList<String> type = FXCollections.observableArrayList();

        for(int i =0; i < Appointments.size(); i++){
            Appointments.get(i).getType();
            if(!type.contains(Appointments.get(i).getType())){
                type.add(Appointments.get(i).getType());
            }
        }
    }

Answer 1

尝试 Java 8 流 API:

ObservableList<Appointment> Appointments = appointmentDOA.findAll();

Map<String, Long> appointmentsMap = appointments.stream()
            .collect(Collectors.groupingBy(Appointment::getType, Collectors.counting()));

您将获得一个 map ，其中约会类型(字符串)作为键，计数作为值。此外，我建议对约会类型使用 Java 枚举:

enum AppointmentType {General, Review, Weekly};

ObservableList<Appointment> Appointments = appointmentDOA.findAll();

Map<AppointmentType, Long> appointmentsMap = appointments.stream()
            .collect(Collectors.groupingBy(Appointment::getType, Collectors.counting()));