Does the shopping cart model encapsulate shopping cart items?

Question

I'm currently preparing to take my Magento Certified Developer test next Tuesday. A couple of the practice tests I have encountered have the following question:

Which object never encapsulates any shopping cart items?
A. Mage_Checkout_Model_Cart
B. Mage_Sales_Model_Quote
C. Mage_Sales_Model_Quote_Address<type=shipping>
D. Mage_Sales_Model_Quote_Address<type=billing>
Answer: B

Why would that be the correct answer? Mage_Sales_Model_Quote has shopping cart items that are associated with it ($_items property, getAllItems() and getItemsCollection() methods). Perhaps I don't properly understand what is meant by encapsulation - what would be the meaning of encapsulation in this context?

Answer 1

(B) makes the least sense. (A), (C) and (D) all give transitive access to shopping cart items through getQuote()->getItemsCollection(), but the quote itself (B) is the object that encapsulates the item collection.

To me that looks like there's a mistake in the practice question and the "never" should not be there.

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About "encapsulation": In software development this is related to information hiding and usually refers to private properties.

Answer 2

I'm not a native english speaker but to me here "encapsulate" means "contain".

I think the answer to this question is Mage_Checkout_Model_Cart. As you can see from this class, it never encapsulates any shopping cart items but it encapsulates quotes (from Mage_Sales_Model_Quote) which themselves encapsulates shopping cart items.