What is refactoring?

Refactoring is the process of restructuring code, while not changing its original functionality. The goal of refactoring is to improve internal code by making many small changes without altering the code's external behavior.

Computer programmers and software developers refactor code to improve the design, structure and implementation of software. Refactoring improves code readability and reduces complexities. Refactoring can also help software developers find bugs or vulnerabilities hidden in their software.

The refactoring process features many small changes to a program's source code. One approach to refactoring, for example, is to improve the structure of source code at one point and then extend the same changes systematically to all applicable references throughout the program. The thought process is that all the small, behavior-preserving changes to a body of code have a cumulative effect. These changes preserve the software's original behavior and do not modify its behavior.

Martin Fowler, considered the father of refactoring, consolidated many best practices from across the software development industry into a specific list of refactorings and described methods to implement them in his book Refactoring: Improving the Design of Existing Code.

What is the purpose of refactoring?

Refactoring improves code by making it:

  • More efficient by addressing dependencies and complexities.
  • More maintainable or reusable by increasing efficiency and readability.
  • Cleaner so it is easier to read and understand.
  • Easier for software developers to find and fix bugs or vulnerabilities in the code.

Code modification is done without changing any functions of the program itself. Many basic editing environments support simple refactorings like renaming a function or variable across an entire code base.

The refactoring process of making multiple minor mods.
This image shows the process of making several small code refactorings.

When should code be refactored?

Refactoring can be performed after a product has been deployed, before adding updates and new features to existing code, or as a part of day-to-day programming.

When the process is performed after deployment, it is normally done before developers move on to the next project. An organization may be able to refactor more code at this point in the software delivery lifecycle, where the developers have increased availability and more time to work on the source code changes needed.

A better time to perform refactoring, though, is before adding updates or new features to existing code. When performed at this point, refactoring makes it easier for developers to build onto the existing code because they are going back and simplifying the code, making it easier to read and understand.

When an organization has a strong grasp on the refactoring process, it can make it a regular process. Whenever a developer needs to add something to a code base, they can look at the existing code to see if it is structured in a way that would make the process of adding new code straightforward. If it is not, then the developer can refactor the existing code. Once the new code is added, the developer can refactor the same code again to make it clearer.

What are the benefits of refactoring?

Refactoring can provide the following benefits:

  • Makes the code easier to understand and read because the goal is to simplify code and reduce complexities.
  • Improves maintainability and makes it easier to spot bugs or make further changes.
  • Encourages a more in-depth understanding of code. Developers have to think further about how their code will mix with code already in the code base.
  • Focus remains only on functionality. Not changing the code's original functionality ensures the original project does not lose scope.

What are the challenges of refactoring?

Challenges do come with the process, however. Some of these include:

  • The process will take extra time if a development team is in a rush and refactoring is not planned for.
  • Without clear objectives, refactoring can lead to delays and extra work.
  • Refactoring cannot address software flaws by itself, as it is made to clean code and make it less complex.

Techniques to perform code refactoring

Organizations can use different refactoring techniques in different instances. Some examples include:

  • Red, green. This widely used refactoring method in Agile development involves three steps. First, the developers determine what needs to be developed; second, they get their project to pass testing; and third, they refactor that code to make improvements.
  • Inline. This technique focuses on simplifying code by eliminating unnecessary elements.
  • Moving features between objects. This technique creates new classes, while moving functionality between new and old data classes.
  • Extract. This technique breaks down code into smaller pieces and then moves those pieces to a different method. Fragmented code is replaced with a call to the new method.
  • Refactoring by abstraction. This technique reduces the amount of duplicate code. This is done when there is a large amount of code to be refactored.
  • Compose. This technique streamlines code to reduce duplications using multiple refactoring methods, including extraction and inline.

Code refactoring best practices

Best practices to follow for refactoring include:

  • Plan for refactoring. It may be difficult to make time for the time-consuming practice otherwise.
  • Refactor first. Developers should do this before adding updates or new features to existing code to reduce technical debt.
  • Refactor in small steps. This gives developers feedback early in the process so they can find possible bugs, as well as include business requests.
  • Set clear objectives. Developers should determine the project scope and goals early in the code refactoring process. This helps to avoid delays and extra work, as refactoring is meant to be a form of housekeeping, not an opportunity to changes functions or features.
  • Test often. This helps to ensure refactored changes do not introduce new bugs.
  • Automate wherever possible. Automation tools make refactoring easier and faster, thus, improving efficiency.
  • Fix software defects separately. Refactoring is not meant to address software flaws. Troubleshooting and debugging should be done separately.
  • Understand the code. Review the code to understand its processes, methods, objects, variables and other elements.
  • Refactor, patch and update regularly. Refactoring generates the most return on investment when it can address a significant issue without taking too much time and effort.
  • Focus on code deduplication. Duplication adds complexities to code, expanding the software's footprint and wasting system resources.

Learn how to refactor code without delaying the deployment process in this article.

This was last updated in September 2021

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