A simple PHP implementation of a Queue

Queue.php

<?php

class Node {

    public $data;
    public $next;

    public function __construct($data)
    {
        $this->data = $data;
        $this->next = NULL;

    }

    public function getData() {
        return $this->data;
    }

}


class Queue {

    private $head;
    private $tail;

    public function __construct()
    {
        $this->head = $this->tail = NULL;
    }

    public function enqueue($data) {
        $new = new Node($data);
        if($this->tail == NULL) {
            $this->head = &$new;
        }
        else {
            $this->tail->next = &$new;
        }
        $this->tail = &$new;
    }

    public function isEmpty() {
        return $this->tail == NULL;
    }

    public function dequeue() {
        if($this->isEmpty()) throw new Exception("The queue is empty");
        $head = $this->head;
        $this->head = $this->head->next;
        return $head->getData();
    }


    public function listQueue() {
        $current = $this->head;
        while ($current != NULL) {
            echo $current->getData()."->";
            $current = $current->next;
        }
        echo "NULL\n";
    }


}


$q = new Queue();
$q->enqueue(3);
$q->enqueue(9);
$q->listQueue();

$q->enqueue(2);
$q->listQueue();
echo 'de-queueing '.$q->dequeue()."\n";
$q->listQueue();