设计模式20-中介者模式

1.场景问题解决

1.1 场景描述

智慧房屋公司的产品：
闹钟、咖啡机、电视机、窗帘等

思考如何设计：
各对象有几种状态改变
相互作用如何

1.2 OO设计

1.3 需求变动

1.4 带来问题

2.用设计模式改进

2.1 分析

2.2 重新设计

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2.3 源码

vo 该package为同僚相关对象
- Colleague 同僚,抽象父类
- Alarm 闹钟继承Colleague
- CoffeeMachine 咖啡机继承Colleague
- Curtains 窗帘继承Colleague
- TV 电视继承Colleague

public abstract class Colleague {private Mediator mediator;public String name;public Colleague(Mediator mediator, String name) {this.mediator = mediator;this.name = name;}public Mediator GetMediator() {return this.mediator;}public abstract void SendMessage(int stateChange);
}public class Alarm extends Colleague {public Alarm(Mediator mediator, String name) {super(mediator, name);mediator.Register(name, this);}public void SendAlarm(int stateChange) {SendMessage(stateChange);}@Overridepublic void SendMessage(int stateChange) {this.GetMediator().GetMessage(stateChange, this.name);}
}public class CoffeeMachine extends Colleague {public CoffeeMachine(Mediator mediator, String name) {super(mediator, name);mediator.Register(name, this);}@Overridepublic void SendMessage(int stateChange) {this.GetMediator().GetMessage(stateChange, this.name);}public void StartCoffee() {System.out.println("It's time to startcoffee!");}public void FinishCoffee() {System.out.println("After 5 minutes!");System.out.println("Coffee is ok!");SendMessage(0);}
}public class Curtains extends Colleague {public Curtains(Mediator mediator, String name) {super(mediator, name);mediator.Register(name, this);}@Overridepublic void SendMessage(int stateChange) {this.GetMediator().GetMessage(stateChange, this.name);}public void UpCurtains() {System.out.println("I am holding Up Curtains!");}
}public class TV extends Colleague {public TV(Mediator mediator, String name) {super(mediator, name);mediator.Register(name, this);}@Overridepublic void SendMessage(int stateChange) {this.GetMediator().GetMessage(stateChange, this.name);}public void StartTv() {System.out.println("It's time to StartTv!");}public void StopTv() {System.out.println("StopTv!");}
}

Mediator 中介者接口
- ConcreteMediator 中介者实现类

public interface Mediator {//注册同僚public abstract void Register(String colleagueName, Colleague colleague);//得到消息后的中介者需要做的操作public abstract void GetMessage(int stateChange, String colleagueName);public abstract void SendMessage();
}public class ConcreteMediator implements Mediator {//注册超类同僚private HashMap<String, Colleague> colleagueMap;//注册子类同僚private HashMap<String, String> interMap;public ConcreteMediator() {colleagueMap = new HashMap<String, Colleague>();interMap = new HashMap<String, String>();}@Overridepublic void Register(String colleagueName, Colleague colleague) {colleagueMap.put(colleagueName, colleague);if (colleague instanceof Alarm) {interMap.put("Alarm", colleagueName);} else if (colleague instanceof CoffeeMachine) {interMap.put("CoffeeMachine", colleagueName);} else if (colleague instanceof TV) {interMap.put("TV", colleagueName);} else if (colleague instanceof Curtains) {interMap.put("Curtains", colleagueName);}}//得到消息后的中介者需要做的操作@Overridepublic void GetMessage(int stateChange, String colleagueName) {if (colleagueMap.get(colleagueName) instanceof Alarm) {if (stateChange == 0) {((CoffeeMachine) (colleagueMap.get(interMap.get("CoffeeMachine")))).StartCoffee();((TV) (colleagueMap.get(interMap.get("TV")))).StartTv();} else if (stateChange == 1) {((TV) (colleagueMap.get(interMap.get("TV")))).StopTv();}} else if (colleagueMap.get(colleagueName) instanceof CoffeeMachine) {((Curtains) (colleagueMap.get(interMap.get("Curtains")))).UpCurtains();} else if (colleagueMap.get(colleagueName) instanceof TV) {} else if (colleagueMap.get(colleagueName) instanceof Curtains) {}}@Overridepublic void SendMessage() {}
}

MediatorTest 测试类

public class MediatorTest {public static void main(String[] args) {Mediator mediator = new ConcreteMediator();Alarm mAlarm = new Alarm(mediator, "mAlarm");CoffeeMachine mCoffeeMachine = new CoffeeMachine(mediator,"mCoffeeMachine");Curtains mCurtains = new Curtains(mediator, "mCurtains");TV mTV = new TV(mediator, "mTV");mAlarm.SendAlarm(0);mCoffeeMachine.FinishCoffee();mAlarm.SendAlarm(1);}
}

3.设计模式总结

3.1 定义

中介者模式：用一个中介对象来封装一系列的对象交互。
中介者使各对象不需要显式地相互引用，从而使其耦合松散，而且可以独立地改变它们之间的交互

3.2 分析思路

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3.3 优缺点

优点：
通过将对象彼此解耦，可以增加对象的复用性
通过将控制逻辑集中，可以简化系统维护
可以让对象之间所传递的消息变得简单而且大幅减少
提高系统的灵活性，使得系统易于扩展和维护
缺点：
中介者承担了较多的责任，一旦中介者出现了问题，整个系统就会受到影响
如果设计不当，中介者对象本身变得过于复杂

4. 设计模式使用场景及注意

4.1 适用场合：

一组对象之间的通信方式比较复杂，导致相互依赖，结构混乱
一个对象引用很多其他对象并直接与这些对象通信，导致难以复用该对象

5.参考文章

内容总计于HeadFirst设计模式及相关视频