将类类型传递给筛选函数

Question

我正在尝试按房间类别（手术室或技术室）返回过滤后的房间列表。有没有办法将room类作为参数传递给getAvailableRooms（）而不是两个私有方法？

import java.util.*;

public class RoomBooker {

    private List<IRoom> rooms = new ArrayList<>();

    public RoomBooker() {
        // Demo data
        rooms.add(new SurgeryRoom("Surgery 1"));
        rooms.add(new SurgeryRoom("Surgery 2"));
        rooms.add(new TechRoom("TechRoom 1"));
        rooms.add(new TechRoom("TechRoom 2"));
    }

    private List<IRoom> filterBySurgeryRoom() {
        List<IRoom> r = new ArrayList<>();
        for (IRoom room : rooms) {
            if (room instanceof SurgeryRoom) {
                r.add(room);
            }
        }
        return r;
    }

    private List<IRoom> filterByTechRoom() {
        List<IRoom> r = new ArrayList<>();
        for (IRoom room : rooms) {
            if (room instanceof TechRoom) {
                r.add(room);
            }
        }
        return r;
    }

    public List<IRoom> getAvailableRooms(String roomType, Date date) {  
        List<IRoom> available = new ArrayList<>();

        switch (roomType.toUpperCase()) {
            case "SURGERY":
                available = filterBySurgeryRoom();
                break;
            case "TECH":
                available = filterByTechRoom();
                break;
        }

        return available;
    }
}




Answer 1

使方法接受Predicate参数，即：

private List<IRoom> filterRoomByType(Predicate<IRoom> predicate) {
        List<IRoom> r = new ArrayList<>();
        for (IRoom room : rooms) {
            if (predicate.test(room)) {
                r.add(room);
            }
        }
        return r;
}

因此，现在每当您调用方法filterRoomByType时，您都可以传入一个函数，该函数定义了if条件的条件。

filterRoomByType(e -> e instanceof SurgeryRoom);

或者

filterRoomByType(e -> e instanceof TechRoom);

Answer 2

您可以使用JavaStreams轻松实现这一点

public List<IRoom> getAvailableRooms(Class<? extends IRoom> roomType, Date date) {
    return rooms.stream().filter(roomType::isInstance).collect(Collectors.toList());
}

并致电：

List<IRoom> list = getAvailableRooms(SurgeryRoom.class, new Date(1234));
List<IRoom> list = getAvailableRooms(TechRoom.class, new Date(1234));

稍后，当您添加日期过滤器时，您可以使用相同的方法，只需改进过滤器部分

如获取特定类别的所有房间以及参数中日期晚于日期的房间：

public List<IRoom> getAvailableRooms(Class<? extends IRoom> roomType, Date date) {
    return rooms.stream()
            .filter(roomType::isInstance)         //== .filter(r->roomType.isInstance(r))
            .filter(r -> r.getDate().after(date))
            .collect(Collectors.toList());
}

Answer 3

将类作为参数传入，并使用此处记录的isInstance方法：https://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#isInstance（java.lang.Object）

private <T extends IRoom> List<T> filterRoomByType(Class<T> roomType) {
    List<T> r = new ArrayList<>();
    for (IRoom room : rooms) {
        if (roomType.isInstance(room)) {
            r.add((T) room);
        }
    }
    return r;
}