Grokking the Object Oriented Design Interview

It is a course on answering object oriented design questions, the round where you are asked to design something like a parking lot or a chess game and produce classes, relationships, and code rather than servers and databases. It covers the object oriented and UML groundwork first, teaches a repeatable method for answering these questions, then works through 22 complete case studies, each one going from requirements to a use case diagram, a class diagram, activity diagrams, and finally a working implementation.

Software engineers preparing for an object oriented design or low level design round, at any level from new graduate upward. It also suits engineers who write code every day but have never had to defend a class design out loud, and anyone who can produce a working solution but freezes when asked to draw the model behind it.

A system design interview asks how a product scales: services, databases, caches, queues, and the trade-offs between them. An object oriented design interview zooms all the way in on one application and asks how it is modelled: which classes exist, what each one is responsible for, how they relate, and what the code looks like. Same product, very different altitude, and preparing for one does not prepare you for the other.

Yes. Object oriented design, OOD, low level design, and LLD are different names companies use for the same round, and machine coding rounds are usually this interview with a working program required at the end. The material here applies to all of them.

The 22 case studies are the classic low level design questions: a parking lot, a library management system, an ATM, an elevator system, a vending machine, a movie ticket booking system, a hotel management system, a car rental system, a restaurant management system, an airline management system, blackjack and a deck of cards, chess, Stack Overflow, Cricinfo, LinkedIn, Facebook, the Amazon online shopping system, an online stock brokerage system, Splitwise, a notification service, an in-memory cache, and a ride sharing service.

Python, Java, and C++. The design work itself is language independent, so you can follow along in any object oriented language, but the implementations are given in those three.

Yes. The method chapter has a dedicated lesson on the design patterns that come up in this round, and twelve case studies end with a short section naming the patterns used in that design: Strategy, State, Template Method, Observer, Decorator, and Singleton. Each pattern appears inside a design you have just worked through, not as an isolated definition.

No. The course teaches the UML it uses before any of the case studies rely on it, with dedicated lessons on use case diagrams, class diagrams, activity diagrams, and sequence diagrams. You need to be comfortable writing object oriented code, but you do not need to have drawn a diagram before.

It opens with a short introduction: what this round is, one complete answer worked end to end before any theory, and a study plan for the time you actually have. Then 7 lessons on object oriented fundamentals and the UML notation you will use, each of the four principles shown with a diagram and running code. Then comes the method: 6 lessons on how to answer one of these questions, covering how to bound the requirements, how to find the classes, how to choose the relationship between two of them, how to check the result against the SOLID principles, and which design patterns come up in this round. The rest is 22 case studies that all follow the same five steps: system requirements, use case diagram, class diagram, activity diagrams, and code. The UML chapter and the method chapter each close with an assessment, the case studies carry five more, and a final exam draws on the whole course. Because every case study runs in the same order, the process becomes something you can repeat under pressure rather than something you have to remember.

There are eight assessments holding 270 questions in total: one closing the UML chapter, one closing the method chapter, five across the case studies grouped by family, and a final exam over the whole course. They are adaptive, so a chapter assessment draws 14 questions from a bank of 30 at your level as you go, and the final exam draws 25 from a bank of 60. Almost none of them ask you to recall a definition. Each one puts you inside a decision, such as which class should own a fact or which relationship belongs on a line, and every option carries a written explanation, including the ones you did not choose.

Text-based, with more than 250 diagrams and code you can read in place. That suits design work better than video, because you will spend most of your time comparing a class diagram against its implementation, and going back and forth between the two is far easier on a page than in a timeline.

Yes. Design Gurus issues a certificate once you have completed the course, and you can share the link directly or add it to your LinkedIn profile.