Design and Implement a Shopping Cart Object Model for an Online Store

Design and implement a shopping cart for an online store, using object-oriented code in a language of your choice. This is a phone-screen object-oriented design exercise, so the goal is a small, runnable model rather than a distributed system.

The cart must let a shopper:

• add a product to the cart with a quantity;
• change the quantity of a product that is already in the cart;
• remove a product from the cart;
• list what is in the cart; and
• get the cart's total price.

Products come from a catalog that the cart can look up by product ID. Each product has at least an ID, a display name and a unit price. Write the classes, implement the operations, and show a short usage example or tests that exercise them.

Constraints and Clarifications

• Assume one shopper using one cart in one process. Persistence, checkout and payment are out of scope unless the interviewer extends the problem.
• Money must be computed exactly; state how you represent it.

Clarifying Questions

• If the shopper adds a product that is already in the cart, should the quantities be merged, or should the call replace or reject the existing line?
• Should setting a quantity to zero remove the line, or is zero an error?
• Should an unknown product ID, a negative quantity or a non-integer quantity raise an error, be ignored, or be clamped?
• Is a product's price fixed when it is added to the cart, or read from the catalog when the total is computed?
• Does the cart need to check inventory when items are added, or only at checkout?
• Are discounts, coupons or taxes part of the total in this version?