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Refactoring in software engineering is reorganizing code without affecting its original functionality. Refactoring aims to improve internal code by making modest changes that do not affect the code's exterior behaviour. Computer programmers and software developers refactor code to improve software design, structure, and implementation.

As a result, Refactoring increases code readability while decreasing complications. Refactoring can also assist software engineers in locating faults or vulnerabilities in their code.

Introduction to Refactoring in Software Engineering

Refactoring in software engineering is a systematic process of enhancing code without adding new functionality that can turn chaos into clean code and a basic design. The refactoring process involves numerous minor changes to a program's source code.

For example, one technique for refactoring is to enhance the structure of source code at one point and then progressively extend the same modifications to all appropriate references throughout the program. The thought process is that all of the modest, behaviour-preserving alterations to a body of code add up to display a cumulative effect. These adjustments keep the software's original behaviour and do not change it. In his book, Refactoring: Improving the Design of Existing Code, Martin Fowler, considered the father of refactoring, gathered many best practices from throughout the software development industry into a specific list of refactorings and detailed techniques to perform them.

Why should We Refactor Our Code When it Works Fine?

The purpose of refactoring in software engineering is not to create new or delete functionalities. Instead, the primary purpose of refactoring is to reduce technical debt and make code easier to maintain in the future. We refactor because we realize the difficulty of getting the design right the first time.

What is Technical Debt?

Ward Cunningham proposed the notion of "technical debt" about the unclean code.

  • If you obtain a bank loan, you can purchase more quickly. However, you pay an additional fee to expedite the procedure; you pay off the principal and the additional interest on the loan. Needless to say, you can accumulate so much interest that it exceeds your whole income, making complete repayment unattainable.
  • The same may be said about code. You can temporarily accelerate development without creating tests for new features, but this will gradually limit your progress until you pay off the debt by writing tests.

Advantages of Refactoring

Refactoring Makes your Code Easier to Modify

Simply put, refactoring is used to improve the design of your software. Any application that is actively being developed is a moving target. Cohesion reduces as new functionality is added. Abstractions are no longer as clean. By refactoring regularly, you change the code to reflect a better grasp of the domain. This alignment makes modification easier.

Refactoring Makes Your Code Easier to Understand

You also make the code easier to understand by improving the design. It is common knowledge that developers read code far more frequently than they write. As a result, it's in everyone's best interest to keep things as simple as possible, which considerably improves maintainability. People who read it in the future will be grateful.

Refactoring is Sharing Knowledge

Finally, refactoring in software engineering is a method of knowledge transfer. Even if you didn't write the code, refactoring it gives you a better grasp of what it accomplishes. When operating as a team, it is critical to share knowledge.

When do we Refactor?

Refactoring can be Done while Adding a New Feature

Refactoring in software engineering allows you to comprehend the code of others better. If you have to deal with dirty code written by someone else, try to refactor it first. Clean code is considerably easier to comprehend. It will also help future developers. Refactoring facilitates the addition of new functionalities. Changes are significantly easier to make in clean code.

Refactoring can be Done while Fixing Bugs

Bugs in code behave similarly to bugs in real life: they reside in the darkest, dirtiest corners of the code. If you clean up your code, the errors will almost certainly reveal themselves. Managers like proactive refactoring because it minimizes the need for special refactoring tasks in the future.

Refactoring can be Done During a Code Review

The code review may be the last opportunity to clean up the code before it is made public. It is ideal to do such reviews in collaboration with an author. This allows developers to swiftly solve fundamental problems while estimating the time required to solve more challenging ones.

How to Identify Code to Refactor?

Martin Fowler proposed that "code smells" be used to determine when and where to refactor. A code smell is any lousy trait in a program's source code that may signal a more significant problem. Determining what is and is not a code smell is subjective and varies depending on the language, developer, and development approach used.


Following are some broad classes of code smells:


Bloaters are codes, methods, and classes that have grown to such massive proportions that they are challenging to deal with. Typically, these smells do not appear immediately but rather collect over time as the program evolves.

Object-Orientation Abusers

These are the incomplete or incorrect applications of object-oriented programming principles. For example, two classes achieve the same tasks but with different names.

Change Preventers

These smells indicate that if you need to modify something in one place in your code, you must also make numerous changes in other locations. As a result, program development becomes substantially more complicated and costly.


A dispensable is something unnecessary whose removal would make the code simpler, more efficient, and easier to understand.


These are code smells that contribute to an excessive coupling between classes or show what happens if the coupling is replaced by excessive delegation.

Refactoring Techniques

Red Green Refactoring

Refactoring is a core engineering technique that supports Test Driven Development, or TDD for short. When it comes to refactoring refers to a fundamental approach that divides the entire procedure into three systematic parts.


  1. The word "red" comes first. You must begin this phase by reviewing the precise development you intend to conduct. You can write a test without including any implementation code when you're finished. As a result, it's only normal for the test to fail.
  2. "Green" is the logical continuation of "red". This is where you will work on the proper implementation code, which will subsequently be used to qualify the project via basic testing.
  3. "Refactor", on the other hand, is the location of the transforming magic. You delve deep into the code and uncover all the basic flaws that need to be addressed. The improvement tweaks will come, but only if none introduce new functionality.

Refactoring by Abstraction


Abstraction, in essence, aims to eliminate repetition and redundancy from your code. It accomplishes this with techniques such as extraction, interface creation, class creation, hierarchy, class inheritance, etc. In addition, abstraction likes to implement large-scale code changes gradually rather than all at once. This allows you to continue using the system while the modifications are being made in the background.

Composition Method of Refactoring

A large portion of refactoring is devoted to correctly composing methods. Excessively long methods are typically the source of all harm. The code complexities within these methods mask the execution logic, making the technique incredibly difficult to understand—and even more challenging to change. These refactoring strategies streamline processes, eliminate code duplication, and prepare the path for future advancements. Some of the methods you can use here include Split Temporary Variable, Inline Method, Inline Temp, and Extraction.

Simplifying Method Calls

These techniques make method calls more straightforward to understand. This, in turn, simplifies the interfaces for interaction between classes.

Moving Features Between Objects

There is still hope, even if you have divided functionality throughout distinct classes in a less-than-ideal manner. These refactoring techniques demonstrate how to move functionality between classes safely, build new classes, and conceal implementation details from the public view.

Preparatory Refactoring


This approach is best used when there's a need for refactoring while adding new features to an application. So it's simply a software update with a separate refactoring process. If you discover that the code needs to be altered during the early stages of feature development, you will spare yourself from future technical debt. The end-user cannot see the engineering team's efforts, but the developers working on the application will know the importance of refactoring the code as they construct the application. They can save time, money, and other resources if they only take the time to update the code earlier.

User Interface Refactoring

Developers can make simple changes in UI and refactor the code. For example: align the entry field, apply font, reword in the active voice to indicate the format, use standard button size, increase color contrast, etc.


  • Unfortunately, the software doesn't age well. Because of the ever-changing digital ecosystem, even seemingly excellent source code deteriorates over time. Small minor errors rapidly accumulate into an insurmountable mountain of bugs, resulting in massive system inefficiencies and skyrocketing maintenance costs.
  • Refactoring, or code refactoring in full, is a systematic process of amending previously built source code without introducing new functionalities or altering the fundamental workings of the subject software.
  • Refactoring promotes maintainability and scalability, enhances readability, improves performance, and saves time and money
  • Refactoring in software engineering can occur after a product has been delivered, before adding updates and new features to existing code, or as part of the day-to-day development process.
  • Refactoring can be done before adding updates or new features to old code. Refactoring at this phase makes it easier for developers to build on top of existing code because they are going back and simplifying it.