What is code refactoring?

Why is refactoring necessary?

As software develops, adding new functionality and fixing bugs, the source code tends to become more complex, more difficult to understand and modify. An initially good design can degrade. Refactoring is needed to counter this process of software entropy. It helps to simplify the code, remove duplication, improve variable and method names, break large classes or functions into smaller ones, and generally improve the design, making it easier to continue working on the code.

When to perform refactoring?

Refactoring should not be treated as a separate major phase of the project, but rather as an ongoing activity woven into the daily development work. Good times for refactoring are:

• Before adding new functionality: Tidying up existing code makes it easier to add new logic.
• When new functionality is added: Check if the newly added code can be simplified or better integrated with the rest of the system.
• When fixing bugs: Understanding and fixing a bug often reveals problems in the structure of the code that are worth fixing on occasion.
• During code review (code review): Identify code fragments that need improvement.
• Regularly, in small steps: Applying the “leave the code cleaner than you found it” principle.

Refactoring techniques

There are many well-described, concrete refactoring techniques (maneuvers). Among the most common are:

• Renaming (Rename): Renaming variables, methods, classes to more descriptive and understandable names.
• Method Extraction (Extract Method): Extracting a piece of code from a longer method into a new, smaller method with a clearly defined purpose.
• Class extraction (Extract Class): Moving some fields and methods from one class to a new class when the old class has too many responsibilities (SRP violation).
• Inline Method/Class (Inline Method/Class): The inverse of extraction when a method or class is too small or its responsibility is trivial.
• Replace Magic Number with Symbolic Constant: Replacing number literals with constants with meaningful names.
• Remove Duplication of Code (Remove Duplication): Finding and eliminating duplicate code fragments, e.g. by extracting to a common method or class.

Many modern development environments (IDEs) offer built-in tools to automatically perform many common refactorings.

The role of automated tests

Performing refactoring safely requires having a robust set of automated tests (especially unit and integration tests). These tests act as a safety net to quickly verify that the changes made to the structure of the code have not broken its functionality. Refactoring without adequate test coverage is very risky.

Summary

Code refactoring is an essential practice in modern software development to maintain high internal code quality and manage technology debt. It is a continuous process of improving the structure of existing code without changing its behavior, supported by automated tests. Regular refactoring leads to more readable, flexible and maintainable software.