帮帮我对于这章的内容还是没弄明白

有关任务的问题

清洁服务

Java 核心, 第 4 级, 课程 8

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为什么不能这样写啊

1.实现 cleanAllApartments 方法。
对于 apartments 中的每个对象：
2.对于一间卧室的公寓 (OneRoomApt)，调用 clean1Room 方法。
即，如果传递了 OneRoomApt 对象，则调用 clean1Room 方法。
3.对于两间卧室的公寓 (TwoRoomApt)，则调用 clean2Rooms 方法
即，如果传递了 TwoRoomApt 对象，则调用 clean2Rooms 方法。
4.对于三间卧室的公寓 (ThreeRoomApt)，则调用 clean3Rooms 方法
即，如果传递了 ThreeRoomApt 对象，则调用 clean3Rooms 方法。

要求：

cleanAllApartments 方法必须接受公寓列表作为参数。
对于列表中所有一间卧室的公寓 (OneRoomApt)，cleanAllApartments 方法必须调用 clean1Room 方法。
对于列表中所有两间卧室的公寓 (TwoRoomApt)，cleanAllApartments 方法必须调用 clean2Rooms 方法。
对于列表中所有三间卧室的公寓 (ThreeRoomApt)，cleanAllApartments 方法必须调用 clean3Rooms 方法。
OneRoomApt、TwoRoomApt 和 ThreeRoomApt 类应支持（实现）Apartment 接口。

package zh.codegym.task.task14.task1415; import java.util.ArrayList; import java.util.List; /* 清洁服务 */ public class Solution { public static void main(String[] args) { List<Apartment> apartments = new ArrayList<>(); apartments.add(new OneRoomApt()); apartments.add(new TwoRoomApt()); apartments.add(new ThreeRoomApt()); cleanAllApartments(apartments); } public static void cleanAllApartments(List<Apartment> apartments) { if (apartments instanceof OneRoomApt) { //OneRoomApt oneroomApt = (OneRoomApt) Apartment; Apartment.OneRoomApt(); } else if (apartments instanceof TwoRoomApt) { Apartment.clean2Rooms(); } else if (apartments instanceof ThreeRoomApt) { Apartment.clean3Rooms(); } // 在此编写项目 1-4 的实现 } static interface Apartment { } static class OneRoomApt implements Apartment { void clean1Room() { System.out.println("1 间房完成清理"); } } static class TwoRoomApt implements Apartment { void clean2Rooms() { System.out.println("2 间房完成清理"); } } static class ThreeRoomApt implements Apartment { void clean3Rooms() { System.out.println("3 间房完成清理"); } } }

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Thomas

级别 41 ，Bayreuth，Germany

16 十二月 2023, 13:38

There are several little problems: 1. There is a List passed to the cleanAllApartments method. Now you take that list and test if it is some Apartment. A List never is an Aparment. A List may contain elements that are of the type Apartment (like here). What you are (probably) supposed to do is to iterate over the collection and check each element. 2. A static method is adressed ClassName.methodName() and because you always write classes uppercase you easily can see what you do. An instance method you adress objectName.methodName(). Here you take an object reference and invoke on it the instance method. If you look at the classes, then you see there are no static methods. So if you call a non existant static method that'll give an compile time error. 3. You try to invoke not existing static methods that you expect to be in a child class using a parent reference. But a parent class does not know about properties of the child class. A class just knows about its own and its parents properties. It has no knowledge about its descendants. 4. What to do: a) loop over the List containing Apartment objects.

for (Apartment apartment : apartments)

now you have in each iteration a reference to one apartment object. And as said this object has no functionality (methods) except the ones it inherits from object. b) that's why you now check if apartment is an instance of 1room or 2room apt if one of these checks succeeds, then you need to cast the reference from Apartment to eg OneRoomAparment.

OneRoomApt oneRoomApartment = (OneRoomApt) apartment;

c) That oneRoomApartment object now knows about all the methods of the OneRoomApt class and you can invoke it

oneRoomApartment.clean1Room();

(There may be typos inside the code)

帮帮我 对于这章的内容还是没弄明白

帮帮我对于这章的内容还是没弄明白