Low-Level Design is a vast discipline. Without a structured approach, learners often bounce randomly between topics—studying design patterns before understanding SOLID principles, or attempting complex system designs without grasping basic object modeling. This fragmented learning produces shallow understanding that crumbles under real-world pressure.

This curriculum is designed with intentional structure. Every chapter builds on previous knowledge. Every module progresses from foundational concepts to advanced applications. Understanding this structure helps you learn more effectively, identify dependencies, and navigate the material strategically.

This curriculum is organized into four major parts, each serving a distinct purpose in your learning journey. Think of these as four ascending phases of mastery:

Part I: Foundations establishes the conceptual groundwork. You cannot design well without understanding what LLD is, how OOP works, and how to think in objects. This part answers: What is LLD, and how do we think about design?

Part II: Object-Oriented Programming Deep Dive provides thorough coverage of OOP mechanics—the building blocks of all LLD. This part answers: What are the tools we use to express designs?

Part III: Design Principles & Patterns teaches the accumulated wisdom of software design—SOLID principles, GRASP patterns, and the classic Gang of Four patterns. This part answers: What proven solutions exist for common design problems?

Part IV: Practical Design & Case Studies brings everything together with real-world design exercises, interview preparation, and complete system designs. This part answers: How do we apply everything we've learned to solve real problems?

The Foundations part comprises three carefully sequenced chapters, each establishing essential concepts that later chapters depend upon.

Chapter 1: Introduction to Low-Level Design

This opening chapter answers the fundamental question: What is Low-Level Design? It establishes LLD as the discipline of defining component internals—classes, interfaces, methods, and relationships. It distinguishes LLD from HLD, explains why it matters, and prepares you for both real-world work and interviews.

Chapter 2: Thinking in Objects — Mental Models

Before diving into syntax and patterns, you need to shift your thinking. This chapter teaches you to see the world through an object-oriented lens—identifying objects in problem statements, modeling entities with attributes and behaviors, and understanding object relationships.

Chapter 3: UML & Design Representation

Design exists in the mind, but it must be communicated. This chapter teaches you to express designs visually using UML (Unified Modeling Language). You'll learn to read and create class diagrams, sequence diagrams, and other representations that make designs concrete and shareable.

Why This Sequence?

The progression is intentional:

1. Introduction establishes what we're learning and why
2. Thinking in Objects provides the mental framework for approaching design
3. UML gives us the language to express and communicate designs

By the end of Part I, you'll have a clear understanding of LLD's purpose, a mental model for object thinking, and the vocabulary to express your designs.

With foundational concepts in place, Part II dives deeply into the mechanics of object-oriented programming. This isn't OOP 101—it's the designer's perspective on OOP, examining each concept for its design implications.

The OOP Building Blocks:

The Design Perspective:

Each OOP concept is examined not just for what it does, but for how it serves design goals:

• Encapsulation isn't just data hiding—it's protecting invariants and enabling safe evolution
• Inheritance isn't just code reuse—it's modeling substitutable behavior (Liskov Substitution)
• Polymorphism isn't just syntax—it's the foundation of flexible, extensible systems
• Abstraction isn't just interfaces—it's managing complexity by hiding irrelevant details

By the end of Part II, you'll understand not just how OOP features work, but when and why to use each in your designs.

Part III introduces the accumulated wisdom of decades of software design experience—principles that guide decisions and patterns that solve recurring problems.

Design Principles:

Principles are guidelines for making good design decisions. They don't tell you exactly what to do, but they help you evaluate options and avoid common pitfalls.

Design Patterns:

Patterns are proven solutions to common design problems. The classic Gang of Four patterns, organized by purpose:

Part IV brings together everything from Parts I-III, focusing on practical application. This is where theory meets practice.

The Design Process:

Case Studies:

The curriculum includes detailed design walkthroughs for common interview problems:

Interview Preparation:

The final chapters focus specifically on interview success:

• Chapter 24: LLD Interview Framework — How to approach LLD interviews systematically
• Chapter 25: Communication & Presentation — How to explain your designs clearly
• Chapter 26: Time Management & Common Mistakes — Avoiding pitfalls, managing interview time

Each chapter is divided into modules, and each module focuses on a specific concept or skill. Understanding module structure helps you navigate efficiently.

Module Components:

Every module contains:

Progression Within Chapters:

Modules within a chapter follow a consistent progression:

1. Conceptual Introduction — What is this thing? Why does it exist?
2. Mechanics — How does it work? What are the rules?
3. Design Implications — When should you use it? What trade-offs exist?
4. Common Pitfalls — What mistakes do people make?
5. Practice — Exercises and examples to reinforce learning

This pattern repeats across the curriculum, creating predictable structure that aids learning.

While the curriculum is designed for sequential progression, different goals may warrant different approaches. Here are recommended learning paths based on your objectives:

Path 1: Complete Mastery (Recommended)

Follow the curriculum sequentially from Chapter 1 through Chapter 26. This path provides the most comprehensive understanding and builds knowledge systematically. Ideal for those with time to invest in deep learning.

Timeline: 2-4 months with consistent study

Path 2: Interview Preparation Focus

If preparing for interviews with limited time, prioritize:

1. Chapter 1-2 (Introduction & Object Thinking) — Essential foundation
2. Chapter 4-6 (Classes, Encapsulation, Inheritance) — Core OOP
3. Chapter 10 (SOLID Principles) — Frequently tested
4. Chapter 13-15 (Design Patterns) — Most common patterns
5. Chapter 20-23 (Case Studies) — Direct interview preparation

Timeline: 4-8 weeks intensive

Path 3: Working Developer Deepening

For developers wanting to improve design skills without interview pressure:

• Complete Parts I & II thoroughly
• Focus on SOLID principles
• Study patterns as you encounter relevant problems at work
• Use case studies to practice

Timeline: Ongoing, project-driven

We've mapped the structure of this comprehensive LLD curriculum. Here are the key takeaways:

What's next:

With the curriculum structure understood, the next page focuses on the recommended practice approach. Learning LLD requires active practice, not passive reading. We'll explore how to approach practice effectively, what types of practice yield the best results, and how to maximize retention.