设计模式：状态模式（State）

public interface State
{
    public void bookRoom();
    public void unsubscribeRoom();
    public void checkInRoom();
    public void checkOutRoom();
}

public class Room
{
    private State freeTimeState;
    private State checkInState;
    private State bookedState;

    private State state;

    public Room()
    {
        freeTimeState = new FreeTimeState(this);
        checkInState = new CheckInState(this);
        bookedState = new BookedState(this);
        state = freeTimeState;
    }

    public void bookRoom()
    {
        state.bookRoom();
    }
    public void unsubscribeRoom()
    {
        state.unsubscribeRoom();
    }
    public void checkInRoom()
    {
        state.checkInRoom();
    }
    public void checkOutRoom()
    {
        state.checkOutRoom();
    }

    public String toString()
    {
        return "该房间的状态是:"+getState().getClass().getName();
    }

    public State getFreeTimeState()
    {
        return freeTimeState;
    }

    public void setFreeTimeState(State freeTimeState)
    {
        this.freeTimeState = freeTimeState;
    }

    public State getCheckInState()
    {
        return checkInState;
    }

    public void setCheckInState(State checkInState)
    {
        this.checkInState = checkInState;
    }

    public State getBookedState()
    {
        return bookedState;
    }

    public void setBookedState(State bookedState)
    {
        this.bookedState = bookedState;
    }

    public State getState()
    {
        return state;
    }

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

public class FreeTimeState implements State
{
    private Room hotelManagement;

    public FreeTimeState(Room hotelManagement)
    {
        this.hotelManagement = hotelManagement;
    }
    @Override
    public void bookRoom()
    {
        System.out.println("您已经预定成功了！");
        this.hotelManagement.setState(this.hotelManagement.getBookedState());
    }

    @Override
    public void unsubscribeRoom()
    {
    }

    @Override
    public void checkInRoom()
    {
        System.out.println("您已经入住了！");
        this.hotelManagement.setState(this.hotelManagement.getCheckInState());
    }

    @Override
    public void checkOutRoom()
    {
    }
}

public class CheckInState implements State
{
    private Room hotelManagement;

    public CheckInState(Room hotelManagement)
    {
        this.hotelManagement = hotelManagement;
    }
    @Override
    public void bookRoom()
    {
        System.out.println("该房间已经入住了");
    }

    @Override
    public void unsubscribeRoom()
    {
    }

    @Override
    public void checkInRoom()
    {
        System.out.println("该房间已经入住了");
    }

    @Override
    public void checkOutRoom()
    {
        System.out.println("退房成功");
        this.hotelManagement.setState(this.hotelManagement.getFreeTimeState());
    }
}

public class BookedState implements State
{
    private Room hotelManagement;

    public BookedState(Room hotelManagement)
    {
        this.hotelManagement = hotelManagement;
    }

    @Override
    public void bookRoom()
    {
        System.out.println("该房间已经预定了");
    }

    @Override
    public void unsubscribeRoom()
    {
        System.out.println("成功退订");
        this.hotelManagement.setState(this.hotelManagement.getFreeTimeState());
    }

    @Override
    public void checkInRoom()
    {
        System.out.println("入住成功");
        this.hotelManagement.setState(this.hotelManagement.getCheckInState());
    }

    @Override
    public void checkOutRoom()
    {
    }
}

Room[] rooms = new Room[2];
for(int i=0;i<rooms.length;i++)
{
    rooms[i] = new Room();
}

rooms[0].bookRoom();
rooms[0].checkInRoom();
rooms[0].bookRoom();
System.out.println(rooms[0]);
System.out.println("-------------");

rooms[1].checkInRoom();
rooms[1].bookRoom();
rooms[1].checkOutRoom();
rooms[1].bookRoom();
System.out.println(rooms[1]);

您已经预定成功了！
入住成功
该房间已经入住了
该房间的状态是:design.state.CheckInState
-------------
您已经入住了！
该房间已经入住了
退房成功
您已经预定成功了！
该房间的状态是:design.state.BookedState