Mediator模式

摘要: Mediator模式

内容: Mediator模式看的有些快，基本概念和意思搞明白了。结合实际经验以前还没有碰到过适合用Mediator模式的场景。以后也尽量避免多类多对象之间的相互操作。

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 Mediator

package 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 Colleague

package 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 Colleague

package 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 ColleagueB

package 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()
 {
  ca.change();
  cb.change();
  cc.change();
 }//end showMediatorPattern()
 
 public static void main(String[] args)
 {
  StringBuilder strb = new StringBuilder("The Mediator Pattern!");
  System.out.println(strb.toString());
  MediatorPattern mp = new MediatorPattern();
  mp.showMediatorPattern();
 }//end main()
 
}//end class MediatorPattern

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