设计模式（行为型设计模式—

设计模式（行为型设计模式——状态模式）

状态模式

基本定义

对有状态的对象，把复杂的“判断逻辑”提取到不同的状态对象中，允许状态对象在其内部状态发生改变时改变其行为。

模式结构

Context（环境类）：可以包括一些内部状态。

State（抽象状态类）：所有具体状态的共同接口，任何状态都实现这个相同的接口，状态之间互相转换。

ConcreteState（具体状态类）：用于处理来自Context的请求，每一个ConcreteState都提供了它对自己请求的实现，

代码实现

State 抽象状态类

public interface State {//预定房间void reservationRoom();//退订房间void unsubscribeRoom();//入住void checkinRoom();//退房void checkoutRoom();
}

ConcreteState 具体状态类

空闲状态

@Slf4j
public class FreeState implements State{Room room;public FreeState(Room room) {this.room = room;}/*** 房间状态改变，还需修改内部状态*/@Overridepublic void reservationRoom() {log.info("您已预定房间");room.setState(room.reservationState);}@Overridepublic void unsubscribeRoom() {}@Overridepublic void checkinRoom() {log.info("您已入住成功");room.setState(room.checkinState);}@Overridepublic void checkoutRoom() {}
}

预定状态

@Slf4j
public class ReservationState implements State{Room room;public ReservationState(Room room) {this.room = room;}@Overridepublic void reservationRoom() {log.error("预定失败，该房间已经被预定");}@Overridepublic void unsubscribeRoom() {log.info("您已经取消预定");room.setState(room.freeState);}@Overridepublic void checkinRoom() {log.info("您已入住成功");room.setState(room.checkinState);}@Overridepublic void checkoutRoom() {}
}

入住状态

@Slf4j
public class CheckinState implements State{Room room;public CheckinState(Room room) {this.room = room;}@Overridepublic void reservationRoom() {log.error("预定失败，该房间已经入住");}@Overridepublic void unsubscribeRoom() {}@Overridepublic void checkinRoom() {log.error("入住失败，该房间已经入住");}@Overridepublic void checkoutRoom() {log.info("您已退房");room.setState(room.freeState);}
}

Context 环境类

/**
* 状态模式特点一、除了关联抽象状态，还需要关联我们具体状态。
* 状态模式特点二, 提供所有的抽象与具体的状态类。并且在无参构造方法初始化状态类。
* 还需要提供所有属性的set方法，供状态类使用，需要提供调用状态类的方法。
**/
@Slf4j
public class Room{State state;/*** 状态模式特点一、除了关联抽象状态，还需要关联我们具体状态*/State freeState;State reservationState;State checkinState;//初始化全部状态，且绑定关系public Room() {freeState = new FreeState(this);reservationState = new ReservationState(this);checkinState = new CheckinState(this);state = freeState;}public void setState(State state) {this.state = state;}/*** 核心方法* @return*/public State getState() {return state;}public void setFreeState(State freeState) {this.freeState = freeState;}public void setReservationState(State reservationState) {this.reservationState = reservationState;}public void setCheckinState(State checkinState) {this.checkinState = checkinState;}public void reservationRoom() {state.reservationRoom();}public void unsubscribeRoom() {state.unsubscribeRoom();}public void checkinRoom() {state.checkinRoom();}public void checkoutRoom() {state.checkoutRoom();}public void showCurrState(){log.info("当前房间状态 {}", this.state.getClass().getSimpleName());}
}

测试类

public class Test {public static void main(String[] args) {Room room = new Room();room.reservationRoom();room.showCurrState();room.checkinRoom();room.showCurrState();room.checkinRoom();room.checkoutRoom();room.showCurrState();}
}

输出结果

FreeState - 您已预定房间

Room - 当前房间状态 ReservationState

ReservationState - 您已入住成功

Room - 当前房间状态 CheckinState

CheckinState - 入住失败，该房间已经入住

CheckinState - 您已退房

Room - 当前房间状态 FreeState