<?php
 
class User {
    private $name;
    protected $notifier;
 
    public function __construct($name) {
        $this->name = $name;
    }
    public function setNotifier(INotifier $notifier) {
        $this->notifier = $notifier;
    }
    public function notify() {
        $this->notifier->notify();
    }
}
 
interface INotifier {
    public function notify();
}
 
class EmailNotifier implements INotifier {
    public function notify() {
        echo "Notify by Email";
    }
}
 
class SMSNotifier implements INotifier {
    public function notify() {
        echo "Notify by SMS";
    }
}
 
class FaxNotifier implements INotifier {
    public function notify() {
        echo "Notify by Fax";
    }
}
 
$john = new User('John');
$smith = new User('Smith');
$edward = new User('Edward');
 
$john->setNotifier(new EmailNotifier());
$smith->setNotifier(new SMSNotifier());
$edward->setNotifier(new FaxNotifier());
 
$john->notify();
$smith->notify();
$edward->notify();