中介者模式，我的理解是，你的项目中存在许多级别平等的同事类实例，并且这些实例之间都需要有不同程度的各种交互操作活动。这个时候可以使用中介者模式来降低各同事类的耦合程度，每个同事类都只关心自己需要做什么，把耦合交互的工作交给中介类来完成。这里用了一个模拟电脑播放CD的例子来讲述这个问题。

这是一个标准定义中得中介者模式用例，在实际应用着，可能不需要所有的同事类都继承于一个父类，也不一定中介者类必须持有所有的同事用类。更多的时候中介者实例可能会用Singleton单例模式来设计。

<?php
 //抽象的同事类
 abstract class Colleague{
  private $mediator;
  
  public function __construct($mediator){
   if($mediator instanceof Mediator)
   {
    $this->mediator = $mediator;
   }
   else {
    trigger_error("Input Object isn't Mediator Class Object!",E_USER_ERROR);
   }
  }
  
  public function getMediator(){
   return $this->mediator;
  }
 }
 
 //CD驱动器类
 class CDDriver extends Colleague{
  public function __construct($mediator){
   parent::__construct($mediator);
  }
  
  //数据变量
  private $data;
  
  //获取光驱读取出来的数据
  public function getData(){
   return $this->data;
  }
  
  //读取光盘
  public function readCD(){
   $this->data = "设计模式,值得好好研究";
   //通知主板，自己的状态发生了改变
   $this->getMediator()->changed($this);
  }
  
 }
 
 //CPU类
 class CPU extends Colleague{
  public function __construct($mediator){
   parent::__construct($mediator);
  }
  //视频数据
  private $videoData;
  //声音数据
  private $soundData;
  
  public function getVideoData(){
   return $this->videoData;
  }
  
  public function getSoundData(){
   return $this->soundData;
  }
  
  public function executeData($data){
   $dataArr = explode(",", $data);
   $this->videoData = $dataArr[0];
   $this->soundData = $dataArr[1];
   $this->getMediator()->changed($this);
  }
 }
 
 //显卡类
 class VideoCard extends Colleague{
  public function __construct($mediator){
   parent::__construct($mediator);
  }
  public function showData($data){
   echo '您现在观看的是:'.$data;
  }
 }
 
 //声卡类
 class SoundCard extends Colleague{
  public function __construct($mediator){
   parent::__construct($mediator);
  }
  public function showData($data){
   echo '画外音:'.$data;
  }
 }
 
 //定义中介者模式接口
 interface Mediator{
  public function changed($colleague);
 }
 
 class MotherBoard implements Mediator{
  //定于中介对象需要掌握的所有需要交互的同事类
  private $cdDriver,$cpu,$videoCard,$soundCard;
  
  public function setCdDriver($cdDriver){
   $this->cdDriver = $cdDriver;
  }
  
  public function setCPU($cpu){
   $this->cpu = $cpu;
  }
  
  public function setVideoCard($videoCard){
   $this->videoCard = $videoCard;
  }
  
  public function setSoundCard($soundCard){
   $this->soundCard = $soundCard;
  }
  
  public function changed($colleague){
   if($colleague instanceof CDDriver){
    $this->opeCDDriverReadData($colleague);
   }
   else if($colleague instanceof CPU){
    $this->opeCPU($colleague);
   }
  }
  
  private function opeCDDriverReadData($cd){
   $data = $cd->getData();
   $this->cpu->executeData($data);
  }
  
  private function opeCPU($cpu){
   $videoData = $cpu->getVideoData();
   $soundData = $cpu->getSoundData();
   $this->videoCard->showData($videoData);
   echo '<br>';
   $this->soundCard->showData($soundData);
  }
 }
 
 //创建中介对象：主板
 $mediator = new MotherBoard();
 //创建各同事类:CD驱动，CPU,显卡,声卡
 $cd = new CDDriver($mediator);
 $cpu = new CPU($mediator);
 $videoCard = new VideoCard($mediator);
 $soundCard = new SoundCard($mediator);
 //让中介类知道所有需要交互的同事类
 $mediator->setCdDriver($cd);
 $mediator->setCPU($cpu);
 $mediator->setSoundCard($soundCard);
 $mediator->setVideoCard($videoCard);
 
 $cd->readCD();
?>