observer

<?php
abstract class AbstractObserver
{
    abstract function update(AbstractSubject $subject_in);
}
abstract class AbstractSubject
{
    abstract function attach(AbstractObserver $observer_in);
    abstract function detach(AbstractObserver $observer_in);
    abstract function notify();
}
function writeln($line_in)
{
    echo $line_in . "<br/>";
}
class PatternObserver extends AbstractObserver
{
    public function __construct()
    {
    }
    public function update(AbstractSubject $subject)
    {
        writeln('*IN PATTERN OBSERVER - NEW PATTERN GOSSIP ALERT*');
        writeln(' new favorite patterns: ' . $subject->getFavorites());
        writeln('*IN PATTERN OBSERVER - PATTERN GOSSIP ALERT OVER*');
    }
}
class PatternSubject extends AbstractSubject
{
    private $favoritePatterns = NULL;
    private $observers = array();
    function __construct()
    {
    }
    function attach(AbstractObserver $observer_in)
    {
        //could also use array_push($this->observers, $observer_in);
        $this->observers[] = $observer_in;
    }
    function detach(AbstractObserver $observer_in)
    {
        //$key = array_search($observer_in, $this->observers);
        foreach ($this->observers as $okey => $oval) {
            if ($oval == $observer_in) {
                unset($this->observers[$okey]);
            }
        }
    }
    function notify()
    {
        foreach ($this->observers as $obs) {
            $obs->update($this);
        }
    }
    function updateFavorites($newFavorites)
    {
        $this->favorites = $newFavorites;
        $this->notify();
    }
    function getFavorites()
    {
        return $this->favorites;
    }
}
writeln('BEGIN TESTING OBSERVER PATTERN');
writeln('');
$patternGossiper  = new PatternSubject();
$patternGossipFan = new PatternObserver();
$patternGossiper->attach($patternGossipFan);
$patternGossiper->updateFavorites('abstract factory, decorator,
visitor');
$patternGossiper->updateFavorites('abstract factory, observer,
decorator');
$patternGossiper->detach($patternGossipFan);
$patternGossiper->updateFavorites('abstract factory, observer, paisley');
writeln('END TESTING OBSERVER PATTERN');
?>