System Design Interview Intro - Object-oriented Design Interview

As you start interviewing for software engineering roles, you might come across a type of interview called "Object-Oriented Design" or "Low Level Design." These interviews are less common than the typical product-oriented system design and infrastructure system design interviews, but you'll likely encounter them at companies that heavily use object-oriented programming languages like Java (Amazon is known for conducting such interviews).

What are OOD?

In these interviews, the interviewer will give you a specific use case or scenario, and your task is to design a system that can handle that use case. However, the focus here is not on breaking the problem down into services or describing the backend database. Instead, you'll need to demonstrate your ability to structure the solution using the right classes, adhering to principles like SOLID (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion).

Essentially, you'll be asked to come up with a sensible design for the different components or entities involved in the system and how they should interact with each other.

For example, the interviewer might ask you to design a system for managing a library, where you'd need to think about classes like Book, Member, Loan, and so on, and how they relate to each other. Or you could be asked to design a simplified version of a ride-sharing app, where you'd need to consider classes like Driver, Rider, Trip, and Payment.

The key is to break down the problem into logical components, identify the responsibilities of each component, and organize them into a coherent class structure that follows good object-oriented design principles.

While these interviews might seem daunting at first, they're a great way to showcase your understanding of object-oriented programming and your ability to think through complex systems. With practice and a solid grasp of design patterns and principles, you'll be well-prepared to tackle these types of interviews.

How to prepare for the OOD interview?

Unlike traditional coding interviews, these assessments delve into your ability to architect complex systems, breaking them down into logical components and classes that adhere to fundamental design principles. It's a true test of your understanding of object-oriented programming and your capacity to think through intricate real-world problems.

Preparing for OOD interviews requires a multi-faceted approach. First and foremost, practice is paramount. Immerse yourself in sample questions and problems, working through them diligently and comparing your solutions with those provided by seasoned professionals. This hands-on experience will sharpen your skills and build your confidence.

Simultaneously, invest time in mastering the foundational principles of OOD, such as SOLID (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion). These guidelines will help you craft maintainable and extensible designs that stand the test of time.

However, it's not just about the technical aspects. OOD interviews are also a test of your communication abilities. You'll need to articulate your thought process clearly, explaining your design decisions and rationale. Practice presenting your ideas, using diagrams and whiteboards to illustrate your points effectively.

Collaborative sessions with fellow developers or study groups can provide invaluable feedback and expose you to alternative perspectives, further refining your skills. With dedication, persistence, and a willingness to learn, you'll be well-equipped to tackle these interviews head-on, showcasing your expertise in object-oriented design and paving the way for a successful career in software engineering.

How to ace the OOD interview?

Object-oriented design interviews aren't about proving you know everything. They're about showing you can figure things out. Here's how to do that:

Clarify the problem. Don't assume you understand what the interviewer means. Ask questions about specific use cases, weird edge cases, and what success looks like. This isn't showing weakness, it shows you care about building the right thing.

Explain as you go. Tell a story about your design process. Why are you making these choices? How does this address what the interviewer wants? Interviewers aren't mind readers – help them see how your brain works.

Be willing to change course. If the interviewer critiques your design or suggests something else, don't get defensive. Software is built through iteration. Show you can roll with the punches and adapt your thinking.

Asking insightful questions, storytelling your design, translating complexity into simplicity, and adapting to feedback - these soft skills are just as vital as technical chops. They're the hallmarks of software engineers who don't just crank out code, but design systems that can scale and evolve over time. Master them, and you'll truly shine in your OOD interviews.