Object-Oriented Design Interview
For software engineers preparing for the object-oriented design (low-level design) or machine-coding round. You will be able to turn a vague prompt into requirements, a class model and working core code in 45 minutes, and defend every choice, across eleven fully worked problems. 29 lessons in 14 sections, about 20 hours.
Course Content
Learn what the object-oriented design round tests, where you will meet it, how it is scored, the mistakes that sink candidates, and how to practise with this course. 2 lessons, about 40 minutes.
Work every problem with the same timed five-phase script: clarifying questions, written requirements, finding classes, assigning responsibilities, and coding only the core. 2 lessons, about 60 minutes.
A reference on encapsulation, abstraction, inheritance, polymorphism, composition, SOLID, UML class diagrams and the seven patterns that actually appear in this round, including when not to use one. 3 lessons, about 120 minutes.
Work the classic first problem end to end: vehicles and spot sizes, spot assignment, pluggable pricing, and two cars racing for the last free spot. 2 lessons, about 100 minutes.
Separate a seat from its state in one show, drive bookings through a hold-and-confirm lifecycle, and prevent double booking under concurrency. 2 lessons, about 90 minutes.
Model files and directories as a Composite and build combinable search filters, so new criteria are added without editing existing code. 2 lessons, about 80 minutes.
Model the machine's lifecycle with the State pattern, handle coins, change and refunds safely, and keep the hardware behind interfaces. 2 lessons, about 80 minutes.
The hardest problem in the course: a car state machine, scheduling as a replaceable Strategy, and the dispatch loop that assigns hall requests to cars. 2 lessons, about 100 minutes.
Scope a broad prompt, separate what a product is from the stock of it, and code checkout with inventory reservation, pricing and promotions. 2 lessons, about 90 minutes.
Put win detection where the data lives, make it constant-time with incremental counters, and extend the game to N×N boards, bots and undo. 2 lessons, about 70 minutes.
Model cards, hands and players, score aces correctly, and run the turn flow with player decisions behind a Strategy and casino rule variations kept out of the code. 2 lessons, about 80 minutes.
Recognise a familiar design in a new problem, then build locker allocation, the parcel and locker lifecycles, and secure one-time pickup codes. 2 lessons, about 80 minutes.
Design for correctness over elegance: an ATM state machine, hardware behind small interfaces, cash dispensing that never pays out partially, and recovery when a step fails midway. 2 lessons, about 90 minutes.
The capstone: scope a many-part prompt, model tables, orders and kitchen tickets with interlocking lifecycles, and apply Observer and Command where they earn their place. 2 lessons, about 100 minutes.