Legacy Code Refactoring: Tips, Steps, and Best Practices

Read this guide on how to transform your outdated systems into modern, efficient, and maintainable software with tips, crucial steps, and best practices.

Nobody loves to work on legacy code because it can be a confusing endeavor; at best, it’s time-consuming. But do we now live with the huge repercussions and costs of retaining and utilizing legacy codes as they are?

Legacy code is usually always associated with technical debt—the cost of achieving fast release and optimal speed-to-market time; however, at the expense of providing quality and durable code that will still need to be revamped later. According to Hitachi consulting research, legacy systems hampered the efficiency of at least 90 percent of organizations.

Undoubtedly, legacy code is gradually becoming a significant burden for businesses. A recent survey by the consortium for IT software quality revealed that legacy systems cost firms in the US more than $500 billion in 2018, with higher figures in the ensuing years.

While we may be unable to measure the technical debts and corresponding costs associated with legacy code for individual companies, the pertinent question is, what can be done to avoid them?

There is no fast and easy way to solve problems, but legacy code refactoring is an efficient way to revamp old and previous software systems and optimize their functionality.

Refactoring is one of the ways to simplify or fix a problematic legacy code without necessarily changing the structure or architecture of the code. The problem is that most companies wrongly understand the concept of refactoring, especially the process of refactoring legacy code.

As a leader of an engineering team, I would be glad to walk you through how to refactor legacy code. Let’s begin by explaining what it’s all about.

What Is Refactoring Legacy Code?

Code refactoring is a corrective procedure that entails modifying and rearranging previously written software programs to make them easier to understand, maintain, and more efficient without altering or jeopardizing the program’s functionality.

The end goal of implementing refactoring in a legacy code is to optimize the code and enhance its performance but not change its operations. After a refactoring procedure, the eventual release becomes easier to interpret, manage, and update.

Importantly, you can only implement refactoring if you understand the code’s limits, purpose, and intended operability. After then, the code is tested and reworked piece by piece. Testing and refactoring legacy code are not mutually exclusive, as you cannot do a complete and efficient refactor without unit testing various modules and components.

Many firms and developers make the mistake of executing or using legacy codes without having corresponding tests. After refactoring, developers should test the program to ensure there are no defects.

As emphasized in the introduction, executing legacy codes without first refactoring or repairing is only a disaster waiting to happen.

A very good example is the popular Equifax security breach of 2017, where its database was compromised, and cybercriminals had access to the personal information of roughly 150 million people.

According to the experts, this was one cyber breach that wasn’t meant to happen. The US Government Accountability Office reports explained that the breach was largely a direct consequence of legacy code on the Equifax website. It would later cost the company over $1 billion to resolve the effects of the breach.

A legacy code becomes problematic mostly because of dirty codes, code rot, broken codes, or simply obsolete codes. And, in resolving this issue, refactoring isn’t the only method that can be used. Some experts argue against refactoring and would only suggest rewriting the codes.

We will not be attending to the rewriting vs. refactoring argument. Admittedly, they are both different means to achieve the same end. However, it is important to know the benefits of each concept and when it is best to apply refactoring or rewriting.

Legacy Code Refactoring vs. Code Rewriting

There are situations where incremental changes and continuous iterations get the job done, and at other times, you just need to start from scratch to get your desired results. It is important to know when you should refactor or rewrite. It would help you save time and resources.

There are no specified and definitive rules that decide when you should choose to rewrite or refactor a program. Before deciding, you may need to consider many factors, including timing, available expertise, need, etc. But based on best practices, we shall highlight certain guidelines that would help you make the decision easily.

When You Should Choose To Rewrite

Rewriting is a procedure in which developers discard all existing code and begin a new programming process. Here, the entire code is restructured and redone to reflect the initial functionality and maybe add newer features. Here are reasons why you should consider rewriting:

  • When there are major transitions: You should consider a rewrite if you are making any major transition in your architecture, like migrating from monolith to microservices or migrating angular js to angular. Here, every element of the old program can be recreated from scratch.
  • When the bulk of the code is dirty or inoperational: Sometimes, the entire, or a major part of the code, is outright dirty and inoperational. In such situations, it would be a waste of time to start refactoring; your best solution would be a rewrite. Some experts suggest the 80% rule—that if 80% of the code needs revamping, you should rewrite it.
  • When the framework can no longer be maintained: Why try to fix something that is practically unmaintainable or has become too complicated and expensive to maintain? If the code cannot be maintained, just rebuild it.
  • When the team cannot interpret the code: If the team cannot interpret the previous program, it’s time to rewrite it.

Pros of Rewriting:

  • The program would have updated and recent features.
  • Rewriting would give the program a new look and design.
  • Continuous iteration.
  • A chance to correct previous errors.

Cons of Rewriting:

  • Rewriting often consumes more time.
  • You would spend more resources, including money.
  • You face the risk of missing previous functionality.
  • It may require new expertise or learning a new language.

When You Should Choose Legacy Code Refactoring

Here are reasons why you should refactor legacy code:

  • If you can’t afford to stall continuity: Sometimes, rewriting may mean that you have to shut down operations, which would be detrimental to your business operations. So, rather than close shop and keep your clients waiting, you may implement a progressive refactor.
  • When you need to make the code more readable: Sometimes, software development takes a protracted period, maybe years, to complete, which could mean that a different set of engineers may finish the project. Or, it could just be that the developers who created the program have moved on. In such situations, refactoring is necessary so the new engineers can understand, interpret, and maintain the program.
  • Regulatory requirements: Certain regulatory standards and policies may demand you make upgrades to your system. 
  • System requires new features: The addition of new features, such as languages or bug fixes, often requires a refactoring procedure, and technical updates are critical for your program since they ensure optimal reliability.
  • The need to expand is essential: Assuming the product is functioning, but it takes too long to add new features, or it causes a slew of problems as a result of the upgrade, then you definitely should refactor.
  • Security risks: Legacy programs face the risk of compromise and security breaches. So, to prevent the occurrence of hacks, you should refactor and do regular updates.

Pros of Refactoring:

  • The code becomes more organized and easy to understand.
  • Careful refactoring legacy codes enhance the operation and performance of the program without altering its function.
  • It helps discover bugs and clean up dirt and rots.
  • Saves time and resources.
  • The program becomes easier to maintain and scale.

Cons of Refactoring:

  • You may end up altering the performance and function of the code.
  • It may cost you more time than you imagined.
  • You face the risk of complicating the code rather than simplifying them.

Simple Steps to Refactor Legacy Code Base

Refactoring legacy code is quite an unpleasant task, and most people tend to avoid it because they think it’s not easy to perform. But, it will be wasteful to discard useful legacy codes because you don’t like refactoring. Implementing legacy codes as they are is too risky as it can compromise your product’s operability and security architecture.

So, what is the approach to refactoring legacy codes? We will outline the steps below to learn how to begin refactoring legacy codes.

1. Breakdown the Whole Process

When you glance at the module, the first thing that hits your mind is how to begin and where to begin. Don’t just jump right in; you will get overwhelmed and confused. Breakdown to tiny relative bits. Doing this will help you identify the change points easily.

This phase also necessitates breaking up the huge or monolith classes into smaller groups. After you’ve separated each monolith class, you may create new files and rename all variables following Java modalities.

2. Identify and Remove Dependencies

After you'’ve gained access to the code, the next thing is to identify and remove dependencies; doing this not only makes the program readable. Writing tests becomes easier when dependencies are separated and removed. 

3. Probe Variables and Run Tests

You may adopt various methods to test the codes, but you must have test scripts; otherwise, it would be impossible to probe. During testing, set up data points and compare results. It would be easier to write tests if more accessible access points were available.

4. Identify and Implement the Appropriate Architecture

The information gathered in prior phases will provide sufficient insight into the type of architecture that will be most appropriate for the project. In addition, the smaller components produced in the preceding exercise will come in helpful when implementing an architecture.

Tips and Basic Principles in Legacy Code Refactoring

  • Breakdown the program into smaller and relative clauses.
  • Take it one step at a time.
  • Identify the change areas and write them out.
  • Create a timeline and stick to it.
  • Make use of test cases.
  • Automate the refactoring process where applicable.
  • Analyze and compare the results.
  • Test again.

Legacy Code Refactoring Best Practices 

Refactoring is easier said than implemented; it’s a sensitive matter that may lead to more problems if not handled properly. Don’t forget: the goal is to optimize the program without altering its functions.

Your refactoring needs must be handled by professional engineers who are experienced in refactoring legacy codes. With over twenty years of experience and a team of experts dedicated to recreating legacy programs and creating beauty out of dirty codes, we are proud to say we’re good at what we do.

Here are some tips for getting the job done:

Prepare for the Necessary Implementation

You probably have some cloud migration questions to ask. The ideal start point of migration is to assess the program environment and evaluate its functionality to devise an upgrade strategy. Do backups for libraries and other app setups. 

Follow Small Steps

You should refactor your code in small bits. Make minor adjustments to your program; each small difference improves your program slightly and keeps the application functional.

Run Tests

The refactoring operation should be accompanied by relevant tests to ensure the changes are effective and bug-free.

Refactoring Should not Introduce New Features

Refactoring should not change the operations or functionality of the program. Rather, it makes it better, faster, increases usability, and makes the program more efficient.


Legacy programs and functional applications should be updated regularly. Legacy system upgrades result in increased performance, easier progression, continuing development, and an improved user experience, but a lack of updates allows security breaches.

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