Code Reuse & Libraries

Code Reuse & Libraries

Code reuse is the practice of using existing code rather than writing new code from scratch. It saves time, reduces bugs, and improves consistency across projects.

Levels of Reuse

  +---------------------------------------------------------+
  |              LEVELS OF CODE REUSE                        |
  +---------------------------------------------------------+
  |                                                         |
  |   COPY-PASTE                                            |
  |   - Lowest level, worst practice                        |
  |   - Creates maintenance nightmare                        |
  |                                                         |
  |   FUNCTION/METHOD                                       |
  |   - Extract common logic into a function                |
  |   - First step toward proper reuse                      |
  |                                                         |
  |   CLASS/MODULE                                          |
  |   - Encapsulate reusable functionality                  |
  |   - Provide clean interface                              |
  |                                                         |
  |   LIBRARY                                               |
  |   - Collection of reusable classes/functions            |
  |   - Used via API calls                                  |
  |                                                         |
  |   FRAMEWORK                                             |
  |   - Provides structure and reusable components          |
  |   - Application plugs into the framework               |
  |                                                         |
  +---------------------------------------------------------+

Using Libraries Effectively

  // Instead of writing your own:
  // - Date formatting
  // - HTTP client
  // - JSON parsing
  // - Validation logic

  // Use well-tested libraries:
  // Java: Apache Commons, Guava
  // JavaScript: Lodash, Axios
  // Python: requests, pydantic
  // C++: Boost

  // Example: Using a validation library
  // BAD: Writing custom email validation
  boolean isValidEmail(String email) {
      return email != null &&
             email.contains("@") &&
             email.contains(".");
  }

  // GOOD: Use a well-tested library
  boolean isValidEmail(String email) {
      return EmailValidator.getInstance().isValid(email);
  }

When to Reuse vs Build

• Reuse when the functionality is well-understood and stable
• Build when the requirements are unique to your domain
• Consider the cost of learning a library vs building a solution
• Evaluate library maintenance, community, and documentation

Key Takeaways

• Reuse saves time and reduces bugs through battle-tested code
• Libraries and frameworks are the most effective levels of reuse
• Evaluate libraries before adopting them
• Avoid copy-paste — extract into reusable functions instead