Understand the Big Picture
Start with Documentation
Look for high-level documentation, architecture diagrams, or design documents. Understand the purpose of the system, its key components, and how they interact. If no documentation exists, ask team members or stakeholders for an overview.
Identify Key Features
Familiarize yourself with the major features and functionalities of the system. This will give you context on why certain parts of the code exist.
Understand the Domain
Get a solid grasp of the problem domain. Knowing the business logic or use cases the system is solving will help you understand the code better.
Set Up and Explore the Development Environment
Get the Code Running
Set up the development environment on your machine as early as possible. Go through the setup process carefully, and try running the system locally. This hands-on experience helps you understand the code’s dependencies and configuration.
Experiment with Small Changes
Once the code is running, experiment by making small changes and observing the behavior. This can give you practical insights into how parts of the system work.
Focus on High-Level Architecture First
Explore Key Modules
Start by identifying the main modules or layers in the codebase (e.g., API layer, database layer, core services). Understand their responsibilities and boundaries.
Follow Data Flow
Track the flow of data or user requests through the system. This helps you see how different parts of the system interact.
Understand Dependencies
Identify external dependencies such as third-party libraries, services, or APIs. Understanding what the code relies on externally will provide more context.
Identify and Study Core Components
Focus on Entry Points
Start with critical entry points like controllers (in web applications), public APIs, or key classes that handle user input. Trace these through the system. Identify Critical Paths: Pinpoint important workflows (e.g., login, checkout) and dive deeper into the code handling these processes.
Examine the Data Model
Understand the structure of the database and key data entities. Look at ORM models (if used) or SQL queries to grasp how data is stored and manipulated.
Use Tools for Code Exploration
Code Navigation Tools
Use your IDE’s code navigation features to jump between definitions, references, and dependencies. This helps you trace the flow and relationships between classes, functions, and modules.
Static Analysis Tools
Tools like SonarQube, CodeClimate, or your IDE’s built-in tools can help you identify code complexity, dead code, and potential hotspots.
Visualization Tools
Tools like Sourcegraph or PlantUML can help visualize dependencies, class hierarchies, or database schemas.
Read the Code Incrementally
Start Small
Instead of trying to understand the entire codebase, pick a smaller, more manageable section, such as a feature or module, and dive deep into that.
Follow a Call Stack
If there’s a particular function or method of interest, trace its call stack both upwards (who calls it) and downwards (what it calls). This helps you understand its purpose and context.
Pair with a Teammate / Ask Questions
Pair Programming
Pair with a teammate, either in real-time or asynchronously, to explore different parts of the code. Experienced teammates can provide context that isn’t easily visible in the code itself.
Ask for Clarifications
Don’t hesitate to ask questions. Complex systems often have undocumented nuances, and a quick conversation with a colleague can save you hours of frustration.
Start with Small Contributions
Fix Bugs or Tackle Small Tasks
Start by picking smaller, well-defined tasks like bug fixes or minor feature enhancements. This will help you build confidence and gradually become familiar with the system.
Write Tests
If the codebase has poor test coverage, writing tests can be an excellent way to learn. You’ll gain an understanding of how different parts of the system interact and ensure the code is working as expected.
Document Your Learning
Keep Notes
Document what you learn as you explore the codebase. Create a personal knowledge base with key concepts, tricky parts of the code, or architectural insights.
Contribute to Official Documentation
If you notice gaps in the system’s documentation, contribute to it. It helps reinforce your learning and benefits the team.
Break It Down with Time and Patience
Be Patient
Complex systems take time to understand. Don’t rush; allow yourself time to absorb and learn the system incrementally.
Consistent Review
Revisit the parts of the code you’ve already explored periodically to reinforce your understanding and make connections as your knowledge deepens.
Summary of Steps
- Understand the big picture.
- Set up the environment and run the code.
- Focus on high-level architecture first.
- Identify and study core components.
- Use tools for code exploration.
- Read the code incrementally.
- Pair with teammates and ask questions.
- Make small contributions.
- Document your learning process.
- Be patient and review consistently.