设计模式----Mediator(中介者)模式
GoF：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示地互相引用，从而使其耦合松散，而且可以独立地改变他们之间的交互。
OOD鼓励奖行为封装到各个对象中，也就是将变化点封装。但是有时候这种封装可能会导致对象间有许多连接。极端情况下，每个对象都知道其他所有对象。各个对象之间的交互比较多，每个对象的行为操作都依赖其他对象。修改一个对象的行为，很可能同时涉及到修改很多其他对象的行为。那么这时，可以使用Mediator模式将集体行为封装在一个“中介者”对象中以避免这个问题。使用Mediator模式可以使各个对象间的耦合松散，只要关心每个对象和Mediator的关系，这样使多对多的关系变成了一对多的关系，每个对象都和Mediator联系。降低了系统得复杂性，提高了可扩展性和可修改性。
下面是实例代码：
package Mediator;public abstract class Mediator
...{
public abstract void register(Colleague c, String type); public abstract void changed(String type);
}//end class Mediatorpackage Mediator;public class ConcreteMediator extends Mediator...{ private ColleagueA a; private ColleagueB b; private ColleagueC c; public ConcreteMediator()
...{ //do something....
}//end ConcreteMediator() public void register(Colleague colleague, String str) ...{ if(str.equals("A")) ...{ a = (ColleagueA)colleague; } else if (str.equals("B")) ...{ b = (ColleagueB)colleague; } else if (str.equals("C")) ...{ c = (ColleagueC)colleague; } }//end register(...) public void changed(String type) ...{ if(type.equals("A")) ...{ b.action(); c.action(); } else if (type.equals("B")) ...{ a.action(); c.action(); } else if (type.equals("C")) ...{ a.action(); b.action(); } }//end change(...) }//end class changed(...)package Mediator;public abstract class Colleague...{ public abstract void change(); public abstract void action();}//end class Colleaguepackage Mediator;public class ColleagueA extends Colleague...{ private final String type = "A"; private Mediator med; public ColleagueA(Mediator m) ...{ med = m; med.register(this, type); }//end ColleagueA(...) public void change() ...{ System.out.println("---------- A changed now ! ----------"); med.changed(type); }//end change() public void action() ...{ System.out.println(" A is changed by mediator "); }//end action() }//end class Colleaguepackage Mediator;public class ColleagueB extends Colleague...{ private final String type = "B"; private Mediator med; public ColleagueB(Mediator m) ...{ med = m; med.register(this, type); }//end ColleagueB(...) public void change() ...{ System.out.println("----- B changed now ! -----"); med.changed(type); }//end change() public void action() ...{ System.out.println(" B is changed by mediator "); }//end action() }//end class ColleagueBpackage Mediator;public class ColleagueC extends Colleague...{ private final String type = "C"; private Mediator med; public ColleagueC(Mediator m) ...{ med = m; med.register(this, type); }//end ColleagueC(...) public void change() ...{ System.out.println("----- C changed now ! -----"); med.changed(type); }//end change() public void action() ...{ System.out.println(" C is changed by mediator "); }//end action() }//end class ColleagueC/**//* * MediatorPattern.java * * Created on 2006年5月4日, 下午3:47 * * To change this template, choose Tools | Template Manager * and open the template in the editor. */package Mediator;/** *//** * * @author Administrator */public class MediatorPattern...{ Mediator myMed = new ConcreteMediator(); ColleagueA ca = new ColleagueA(myMed); ColleagueB cb = new ColleagueB(myMed); ColleagueC cc = new ColleagueC(myMed); /** *//** Creates a new instance of MediatorPattern */ public MediatorPattern() ...{ //do something.... }//end MediatorPattern() public void showMediatorPattern()