Hikashop checkout API

I referred to the developer documentation I could only find the samples code provided to load product, add a product to cart, load the order details. But, it does not have the checkout process code samples. Which class should i get? help me out!!!

Thanks for the reply. By the way, I am trying to write my own hikashop services for an Android App. Integrating Hikashop e-commerce into Android App.

There's lot of code. How do i proceed from here?
Say
1. Load a product:
$productClass = hikashop_get('class.product');
$product=$productClass->get($product_id);

2. Add/Update product(s);
$cartClass = hikashop_get('class.cart');
$cartClass->update($product_id,$quantity);

3. Currently, there's no payment integration for the Android App. Its a free product. How do i checkout from here skipping payment integration. Also, i have disabled payment gateway integration in the Hikashop Backend. Do i have to load this class components/com_hikashop/controllers/checkout.php But how?

Thanks.

Hey Nikolas, Thanks for that, i browsed through that code. How do i call this file in my application. Actually, I dont want HTML form to be loaded. I would require a json output from the hikashop, as its an Android App. Later, I will mimic a HTML form in the android app and redirect the user for payment platform. I was wondering do we have any method like say:
$cartClass = hikashop_get('class.cart');
$cartClass->AddToCart($parameters);

Thanks again..., I have included helpers/helper.php as per the Documentation . Sorry, i did not mean Add_to_cart method(I am aware update() method does that), instead i was looking for
$cartClass = hikashop_get('class.cart');
$cartClass->checkout($parameters); //something like this.
or
$cartClass->generateOrder($parameters); //something like this.
or
$cartClass->PaymentProcess($parameters); //something like this.

I am also aware hikashop does not return json objects. Indeed, I am looking for php multi-dimensional arrays(so does $cartClass->update() method).

$order object in save() method has $obj many parameters. Do we have any methods that returns $order object.
Thanks.

As per Hikashop documentation

get($order_id);

$obj = null;
//add params to $obj
$class= hikashop_get('class.order');
$class->save($obj);