I can't add product to shopping cart, please help me!

PHP
1

I’m trying add product to my shopping cart, but with new product, it won’t be created and the quantity of old product is increment, please see my code:

test.php


<?php
    include_once 'cart/Product.php';
    include_once 'cart/ShoppingCartItem.php';
    include_once 'cart/ShoppingCart.php';

    $ford = new Product(1, "ford", 25000, "08/03/2013");
    $rollroy = new Product(2, "roll roy", 26000, "8/3/2013");

    $shopping_cart->addItem($ford);
    $shopping_cart->addItem($ford);
    $shopping_cart->addItem($ford);
    $shopping_cart->addItem($rollroy);

    $allProducts = $shopping_cart->getItems();

    for ($i = 0; $i < count($allProducts); $i++) {
        echo "<br />";
        echo $allProducts[$i]->getProduct()->id."<br />";
        echo $allProducts[$i]->getProduct()->name."<br />";
        echo $allProducts[$i]->getQuantity();
    }

?>

Result is 2 - ford - 4

ShoppingCart.php


<?php
    class ShoppingCart {

        private $items = array();
        private $numberOfItem;
        private $total;

        public function ShoppingCart() {
            $this->numberOfItem = 0;
            $this->total = 0;
        }

        /**
         * Adds ShoppingCartItem to the ShoppingCart
         * If item existed, the quantity is increment and not
         * create new ShoppingCartItem
         *
         * @param Product $product
         * @see ShoppingCartItem
         */
        public function addItem(Product $product) {

            $newItem = true;

            for ($i = 0; $i<count($this->items); $i++) {
                if ($this->items[$i]->getProduct()->getId() == $product->getId()) {
                    $newItem = FALSE;
                    $this->items[$i]->incrementQuantity();
                }
            }

            if ($newItem) {
                $scItem = new ShoppingCartItem($product);
                $this->items[] = $scItem;
            }
        }

    }
?>

ShoppingCartItem.php


<?php
    class ShoppingCartItem {

        private $product;
        private $quantity;

        public function ShoppingCartItem(Product $product) {
            $this->product = $product;
            $this->quantity = 1;
        }

        public function getProduct() {
            return $this->product;
        }

        public function getQuantity() {
            return $this->quantity;
        }

        public function setQuantity($quantity) {
            $this->quantity = $quantity;
        }

        public function incrementQuantity() {
            $this->quantity++;
        }

        public function decrementQuantity() {
            $this->quantity--;
        }

        public function getTotal() {
            $amount = 0;
            $amount = ($this->getQuantity() * (double)$this->product->getPrice());
            return $amount;
        }

    }
?>

and Product.php


<?php
    class Product {
        private $id;
        private $name;
        private $price;
        private $lastUpdate;
        private $category;

        public function Product($id, $name, $price, $lastUpdate) {
            $this->id= $id;
            $this->name = $name;
            $this->price = $price;
            $this->lastUpdate = $lastUpdate;
        }

        public function __get($property) {
            $method = "get{$property}";
            if (method_exists($this, $method)) {
                return $this->$method();
            };
        }

        public function __set($property, $value) {
            $method = "set{$property}";
            if (method_exists($this, $method)) {
                return $this->$method($value);
            }
        }

        public function getId() {
            return $this->id;
        }

        public function setId($id) {
            $this->id = $id;
        }

        public function getName() {
            return $this->name;
        }

        public function setName($name) {
            $this->name = $name;
        }

        public function getPrice() {
            return $this->price;
        }

        public function setPrice($price) {
            $this->price = $price;
        }

        public function getLastUpdate() {
            return $this->lastUpdate;
        }

        public function setLastUpdate($lastUpdate) {
            $this->lastUpdate = $lastUpdate;
        }

        public function getCategory() {
            return $this->category;
        }

        public function setCategory($category) {
            $this->category = $category;
        }
    }
?>
2

I found errors, thank for watching!