第二十五章　中介者模式

中介者模式（Ｍediator）：用一个中介对象来封装一系列的对象交互。中介者使对象不需要显示的相互引用，从而使其耦合松散，而且可以独立的改变它们之间的交互。

优点：Ｍediator的出现减少了各个Colleague的耦合，使得可以独立改变和复用各个Colleague类和Mediator。由于把对象如何协作进行了抽象，将中介作为一个独立的概念并将其封装在一个对象中，这样关注的重点就从对象各自的行为转移到它们之间的交互上来，也就是站在一个更宏观的角度去看待系统。

缺点：由于ConcreteMediator控制了集中化，于是就把交互复杂性变为了中介者的复杂性，这就使得中介者会变得比任何一个ConcreteColleague都复杂。

应用场景：一般应用于一组对象以定义良好但是复杂的方式进行通信的场合；以及想定义一个分布在多个类中的行为，而又不想生成太多子类的场合。

/**
* Created by hero on 16-4-11.
*/
public abstract class Mediator {
public abstract void send(String message, Colleague colleague);
}
/**
* Created by hero on 16-4-11.
*/
public class ConcreteMediator extends Mediator {
private ConcreteColleague1 concreteColleague1;
private ConcreteColleague2 concreteColleague2;

@Override
public void send(String message, Colleague colleague) {
if (colleague instanceof ConcreteColleague1) {
concreteColleague2.notify(message);
} else {
concreteColleague1.notify(message);
}
}

public ConcreteColleague1 getConcreteColleague1() {
return concreteColleague1;
}

public void setConcreteColleague1(ConcreteColleague1 concreteColleague1) {
this.concreteColleague1 = concreteColleague1;
}

public ConcreteColleague2 getConcreteColleague2() {
return concreteColleague2;
}

public void setConcreteColleague2(ConcreteColleague2 concreteColleague2) {
this.concreteColleague2 = concreteColleague2;
}
}
/**
* Created by hero on 16-4-11.
*/
public abstract class Colleague {
protected Mediator mediator;

public Colleague(Mediator mediator) {
this.mediator = mediator;
}
}
/**
* Created by hero on 16-4-11.
*/
public class ConcreteColleague1 extends Colleague {
public void send(String message) {
mediator.send(message, this);
}

public void notify(String message) {
System.out.println("colleague 1 receives message: " + message);
}

public ConcreteColleague1(Mediator mediator) {
super(mediator);
}
}
/**
* Created by hero on 16-4-11.
*/
public class ConcreteColleague2 extends Colleague {
public void send(String message) {
mediator.send(message, this);
}

public void notify(String message) {
System.out.println("colleague 2 receives message: " + message);
}

public ConcreteColleague2(Mediator mediator) {
super(mediator);
}
}
public class Main {

public static void main(String[] args) {
ConcreteMediator mediator = new ConcreteMediator();
ConcreteColleague1 concreteColleague1 = new ConcreteColleague1(mediator);
ConcreteColleague2 concreteColleague2 = new ConcreteColleague2(mediator);
mediator.setConcreteColleague1(concreteColleague1);
mediator.setConcreteColleague2(concreteColleague2);
concreteColleague1.send("吃了吗？");
concreteColleague2.send("没，你请客？");
}
}