Day 1–3: Understand the Basics of OOD
Start with core concepts: understand what Object-Oriented Design (OOD) is and why it’s used in software engineering. Learn about classes, objects, abstraction, encapsulation, inheritance, and polymorphism. Use small Java, Python, or C++ examples to see how these principles work in practice.
Action Plan:
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Read “Head First Object-Oriented Analysis and Design”
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Watch beginner-level OOD tutorials on YouTube or platforms like Coursera/Udemy
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Practice modeling real-world entities like Car, Animal, BankAccount, etc., using OOP
Day 4–6: Learn the 4 Pillars and SOLID Principles
Go deep into the four pillars of OOP (abstraction, encapsulation, inheritance, and polymorphism) and understand how they relate to clean, maintainable software. Next, study the SOLID principles:
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Single Responsibility Principle
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Open/Closed Principle
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Liskov Substitution Principle
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Interface Segregation Principle
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Dependency Inversion Principle
Action Plan:
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Create short examples that violate each SOLID principle and refactor them
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Follow blog posts or GitHub examples illustrating these principles
Day 7–10: Study Design Patterns
Learn common object-oriented design patterns that frequently appear in interviews:
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Creational: Singleton, Factory, Abstract Factory
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Structural: Adapter, Decorator, Composite
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Behavioral: Strategy, Observer, Command
Understand when to use each, not just how they work.
Action Plan:
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Read “Head First Design Patterns”
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Implement 1-2 design patterns per day in your preferred language
Day 11–13: Practice Class Design for Real-World Systems
Try designing classes for common systems:
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Book My Show (movie ticketing)
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Library Management System
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Parking Lot
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Coffee Machine
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Elevator System
Focus on identifying entities, relationships, data structures, class responsibilities, and method design.
Action Plan:
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Use UML diagrams or draw class diagrams on paper
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Practice explaining your designs aloud
Day 14–16: Get Familiar with Low-Level Design Questions
These are detailed design problems that test your understanding of classes, object interactions, and system behavior. Example questions:
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Design a rate limiter
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Design a logger system
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Design a file system
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Design a Tic-Tac-Toe or Snake game
Action Plan:
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Implement one design per day
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Use clean class separation, modular design, and appropriate data structures
Day 17–19: Analyze and Review Popular OOD Interview Problems
Go through curated interview problems from platforms like:
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Design Gurus (Grokking the Object-Oriented Design Interview)
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LeetCode Discuss
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Glassdoor interview experiences
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GitHub repositories for OOD
Action Plan:
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Review 2–3 problems per day
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Note patterns, repeated object relationships, and preferred approaches
Day 20–22: Refine Communication and Trade-Off Analysis
In interviews, you’re judged not only on your design but also on how you explain it. Practice:
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Justifying choices (e.g., why composition over inheritance)
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Explaining trade-offs (simplicity vs flexibility)
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Discussing scalability and maintainability
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Identifying extensibility points in your design
Action Plan:
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Mock interviews with peers or mentors
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Record yourself explaining a design and review for clarity
Day 23–25: Master UML and Diagram Sketching
Even in virtual interviews, visual explanation is vital. Learn:
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Class Diagrams
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Sequence Diagrams
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Component Diagrams
Action Plan:
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Use tools like draw.io, Lucidchart, or just pen and paper
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Redesign previously attempted problems with diagrams
Day 26–28: Timed Practice + Mock Interviews
Simulate actual interview conditions:
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Pick a system design problem
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Time yourself for 45–60 minutes
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Think aloud, draw diagrams, and code interface stubs or pseudocode
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Get feedback from peers or use platforms like Pramp/Interviewing.io
Day 29: Review and Reflect
Revisit your previous designs and review them with a critical eye:
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Are your abstractions consistent?
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Did you follow SOLID principles?
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Is your design modular, testable, and extensible?
Prepare a “cheat sheet” of your most reused patterns, templates for approaching problems, and typical questions to ask interviewers.
Day 30: Relax and Trust Your Process
On the final day, don’t over-cram. Review your top 3–5 design examples, mentally walk through the logic, and practice calmly explaining them. Confidence and clarity are as important as correctness.
Final Tips:
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Always clarify requirements before jumping into design
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Think in terms of interfaces, not implementations
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Emphasize reusability and extensibility
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Make naming and module responsibilities clean and intuitive
With this 30-day roadmap, you’ll build a solid foundation in object-oriented design and significantly improve your performance in system design interviews.