设计模式之中介模式

作用

用一个中介对象来封装一系列的对象交互。中介者使各个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。

原理

Mediator：抽象中介类，定义了同事对象到中介者对象的接口。

ConcreteMediator：具体中介类，实现抽象方法，他需要知道所有的具体的同事类，即以一个集合来管理HashMap，并接受某个同事对象消息，完成相应的任务。

Colleague：抽象同事类

ConcreteColleague：具体的同事类，每个同事只知道自己的行为，而不了解其他同事类的行为（方法），但是他们都依赖中介者对象。

案例

Mediator

public interface Mediator {

    void register(String colleagueName, Colleague colleague);

    void getMessage(int stateChange, String colleagueName);

    void sendMessage();

}

ConcreteMediator

public class ConcreteMediator implements Mediator {

    private Map<String, Colleague> colleagueMap;
    private Map<String, String> interMap;

    public ConcreteMediator() {
        colleagueMap = new HashMap<>();
        interMap = new HashMap<>();
    }

    @Override
    public void register(String colleagueName, Colleague colleague) {
        colleagueMap.put(colleagueName, colleague);
        if (colleague instanceof Alarm) {
            interMap.put("alarm", colleagueName);
        } else if (colleague instanceof TV) {
            interMap.put("tv", colleagueName);
        }
    }

    @Override
    public void getMessage(int stateChange, String colleagueName) {
        if (colleagueMap.get(colleagueName) instanceof Alarm) {
            if (stateChange == 0) {
                String tv = interMap.get("tv");
                TV tvColleague = (TV) colleagueMap.get(tv);
                tvColleague.startTV();
            } else if (stateChange == 1) {
                String tv = interMap.get("tv");
                TV tvColleague = (TV) colleagueMap.get(tv);
                tvColleague.stopTV();
            }
        }
    }

    @Override
    public void sendMessage() {

    }
}

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 mediator;
    }

    public abstract void sendMessage(int stateChange);

}

ConcreteColleague

public class Alarm extends Colleague {

    public Alarm(Mediator mediator, String name) {
        super(mediator, name);
        mediator.register(name, this);
    }

    @Override
    public void sendMessage(int stateChange) {
        getMediator().getMessage(stateChange, this.name);
    }
}

public class TV extends Colleague {

    public TV(Mediator mediator, String name) {
        super(mediator, name);
        mediator.register(name, this);
    }

    @Override
    public void sendMessage(int stateChange) {
        getMediator().getMessage(stateChange, this.name);
    }

    public void startTV() {
        System.out.println("Start TV!");
    }

    public void stopTV() {
        System.out.println("Stop TV!");
    }

}

调用

public class Client {
    public static void main(String[] args) {
        Mediator mediator = new ConcreteMediator();
        Alarm alarm = new Alarm(mediator, "alarm");
        TV tv = new TV(mediator, "tv");
        alarm.sendMessage(0);
        alarm.sendMessage(1);
    }
}