PHP设计模式之观察者模式入门与应用案例详解(2)

<?php
// 主题接口
interface Subject{
  public function register(Observer $observer);
  public function notify();
}
// 观察者接口
interface Observer{
  public function watch();
}
// 主题
class Action implements Subject{
   public $_observers=array();
   public function register(Observer $observer){
     $this->_observers[]=$observer;
   }
   public function notify(){
     foreach ($this->_observers as $observer) {
       $observer->watch();
     }
   }
 }
// 观察者
class Cat implements Observer{
   public function watch(){
     echo "Cat watches TV<hr/>";
   }
 } 
 class Dog implements Observer{
   public function watch(){
     echo "Dog watches TV<hr/>";
   }
 } 
 class People implements Observer{
   public function watch(){
     echo "People watches TV<hr/>";
   }
 }
// 应用实例
$action=new Action();
$action->register(new Cat());
$action->register(new People());
$action->register(new Dog());
$action->notify();