在酒店管理系统中，酒店房间的状态是不断变化：有已预订、已入住、空闲状态。应用状态模式，用Java改进该设计

好的，我理解了你的问题。在酒店管理系统中，酒店房间的状态是不断变化的，可以使用状态模式来改进该设计。状态模式是一种行为模式，它允许对象在其内部状态改变时改变其行为。在这种情况下，酒店房间的状态就是其内部状态，而其行为取决于其状态。

首先，我们需要定义一个状态接口（RoomState），其具有三个方法：预订（book）、入住（checkIn）和退房（checkOut）。然后，我们需要为酒店房间的每种状态实现一个具体状态类，并在这些类中实现这些方法。最后，我们需要在酒店房间类（Room）中维护一个当前状态对象，并在该类中调用当前状态对象的方法。

下面是代码示例：

//定义状态接口
public interface RoomState {
    void book(Room room);
    void checkIn(Room room);
    void checkOut(Room room);
}

//已预订状态
public class BookedState implements RoomState {
    @Override
    public void book(Room room) {
        System.out.println("The room is already booked.");
    }

    @Override
    public void checkIn(Room room) {
        System.out.println("Checking in...");
        room.setState(new CheckedInState());
    }

    @Override
    public void checkOut(Room room) {
        System.out.println("Cannot check out, the room is already booked.");
    }
}

//已入住状态
public class CheckedInState implements RoomState {
    @Override
    public void book(Room room) {
        System.out.println("Cannot book, the room is already checked in.");
    }

    @Override
    public void checkIn(Room room) {
        System.out.println("The room is already checked in.");
    }

    @Override
    public void checkOut(Room room) {
        System.out.println("Checking out...");
        room.setState(new VacantState());
    }
}

//空闲状态
public class VacantState implements RoomState {
    @Override
    public void book(Room room) {
        System.out.println("Booking...");
        room.setState(new BookedState());
    }

    @Override
    public void checkIn(Room room) {
        System.out.println("Cannot check in, the room is not booked.");
    }

    @Override
    public void checkOut(Room room) {
        System.out.println("Cannot check out, the room is already vacant.");
    }
}

//酒店房间类
public class Room {
    private RoomState state;

    public Room() {
        state = new VacantState();
    }

    public void setState(RoomState state) {
        this.state = state;
    }

    public void book() {
        state.book(this);
    }

    public void checkIn() {
        state.checkIn(this);
    }

    public void checkOut() {
        state.checkOut(this);
    }
}

现在我们可以在主函数中测试我们的实现：

public static void main(String[] args) {
    Room room = new Room();

    room.book();
    room.book();
    room.checkIn();
    room.checkOut();
    room.checkOut();
    room.book();
    room.checkIn();
}

输出应该如下所示：

Booking...
The room is already booked.
Checking in...
Checking out...
Cannot check out, the room is already vacant.
Booking...
Checking in...