Refactoring: Improving the Design of Existing Code
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- Create Date：2021-11-19 06:51:04
- Update Date：2025-09-07
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- Author：Martin Fowler
- ISBN：8131734668
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Summary
Refactoring is about improving the design of existing code。 It is the process of changing a software system in such a way that it does not alter the external behavior of the code， yet improves its internal structure。 With refactoring you can even take a bad design and rework it into a good one。 This book offers a thorough discussion of the principles of refactoring， including where to spot opportunities for refactoring， and how to set up the required tests。 There is also a catalog of more than 40 proven refactorings with details as to when and why to use the refactoring， step by step instructions for implementing it， and an example illustrating how it works。 The book is written using Java as its principle language， but the ideas are applicable to any OO language。
For Sale in Indian subcontinent only
For Sale in Indian subcontinent only
Reviews
Fırat Özbay
，
This is by far the most concrete and example driven book I've read on how to write clean code。 And I want to say that this is currently the number one book I would recommend to every software development professional。In summary there are 2 ways to write clean code:1- Use every single brain cell you have before writing your code for the best possible design2- Refactor along as the code matures and requirements changeI have almost always seen that is much safer to go with the second option。The boo This is by far the most concrete and example driven book I've read on how to write clean code。 And I want to say that this is currently the number one book I would recommend to every software development professional。In summary there are 2 ways to write clean code:1- Use every single brain cell you have before writing your code for the best possible design2- Refactor along as the code matures and requirements changeI have almost always seen that is much safer to go with the second option。The book talks about refactorings we do everyday， only gives them proper names and uses them as nouns。 So instead of telling us to 'extract' the method Fowler uses the phrase "Use 'Extract Method'"。 This actually helps you remember the methods by their titles。 This gets useful when he explains more complex refactorings。 He explains the more complex refactorings by using simpler refactorings（which actually feels like re-using code， but now it is a refactoring method）。The only complaint I have with this book is the examples of mirrored refactorings。 The examples did not justify them well。 The codes in the examples were exactly the same but only the before and after had switched places。 I would have preferred examples that made sense to apply the changes instead of a lame excuse that tells me that I might need to do 'this refactoring' in some situations。 But luckily this was only a concern in a few chapters。 Most of the refactorings Fowler applied on the book just made sense and made the code better。Thank you Martin Fowler Sir for writing this book。 I hope we can one day meet each other in real life。 。。。more
Víctor Martínez
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Siento que leí este libro muy tarde en mi carrera， creo que el momento prefecto hubiera sido después de unos dos o tres años de experiencia en desarrollo de software。Si usted revisa código al aprobar por ejemplo un pull request， esta también será una herramienta muy útil。
Dennis Nehrenheim
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Context & Why I read this bookI am a software engineer with a focus on mobile applications and was looking for a more systematic approach to safely rewriting code without causing regressions。 Such methodical "refactoring" is a valuable skill for developers; especially in enterprise settings where one works on large codebases with many contributors。 Further， Addison Wesley & Martin Fowler are renowned in the field of software construction。 What is the book about as a whole？The author himself says Context & Why I read this bookI am a software engineer with a focus on mobile applications and was looking for a more systematic approach to safely rewriting code without causing regressions。 Such methodical "refactoring" is a valuable skill for developers; especially in enterprise settings where one works on large codebases with many contributors。 Further， Addison Wesley & Martin Fowler are renowned in the field of software construction。 What is the book about as a whole？The author himself says that this is a guide for professional programmers on how to refactor code "in a controlled and efficient manner"。 He explains what refactoring is （and what not）， how to do it properly and he gives many detailed and step-by-step code refactoring examples using the programming language JavaScript。 （This review is about the second edition of the book， which appeared 18 years after the first edition， which used Java for code samples）The book's structureThe book is divided into 12 chapters:1。 Refactoring， a First Example（the author deliberately leads with a very practical introduction instead of a theoretical one） 2。 Principles in Refactoring（a more general and theoretical introduction to the concept of changing software systems without causing regressions）3。 Bad Smells in Code（a list of indications that show you _when_ to apply refactoring; unfortunately no code samples in this section） 4。 Building Tests（A dedicated section on automated testing， since refactoring cannot be done without an appropriate test suite）5。 Introducing The Catalog6。 A First Set of Refactorings 7。 Encapsulation8。 Moving Features between Objects 9。 Organizing Data10。 Simplifying Conditional Expressions11。 Refactoring APIs 12。 Dealing with Inheritance Chapters 6-12 make up the "refactoring catalog"， which contains 67 "refactorings" with names like:- "Change Function Declaration"- "Extract Function"- "PullUp Method"- "Replace Loop with Pipeline"Each Refactoring contains a small graphic to memorize the refactoring， followed by a short and glanceable code example and a section on the motivation of the particular refactoring。 Then there is the main part: a section called "mechanics" which is a detailed list of usually 5-12 steps on how to approach the given Refactoring followed by a detailed example with sample code。 The physical book comes with a free digital web version included。 One lessonRather than mentioning a particular refactoring or concrete advice from the book I want to take the lesson with me， that "Refactoring" is no island and only works properly in combination with self-testing code （automated tests）， trunk based development （or continuous integration） and the general philosophy of opportunistically improving a code base little by little。 Reading Recommendation / Who should read this？I think， that this book （in its second edition！） makes a good and valuable contribution by showing you that there is a more methodical and structured way of changing code。 The book will not render you a refactoring expert since most of it （the catalog） is meant for reference instead of up-front learning （while containing many code samples， there are no exercise or challenges to solve and Fowler himself refers to William C。 Wake'" Refactoring Workbook this regard）。 But even if it did， according to my limited experience in the field， in many （if not most） enterprise settings with legacy codebases and large teams there is not much hope that introducing this will ever work （see my lesson above）。 So while at the moment I don't see much practical relevance for myself I still consider it worthwhile to read this book for software engineers。 Also， if you think this is wrong and your company successfully applies this， pls hire me。All in all a 7 out of 10 （⭑⭑⭑⭑） on my personal rating scale （"Good read， despite minor weaknesses; generally recommended。"）-----------Find my other book reviews at: https://www。dennisnehrenheim。com/read 。。。more
Islam Elgohary
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The techniques are kind of trivial for me and the mechanics aren't really that useful。 However， it can be used as a reference books by developers who are encountering legacy code for the first time。 That will certainly make it a lot easier for them to get the job done。 The techniques are kind of trivial for me and the mechanics aren't really that useful。 However， it can be used as a reference books by developers who are encountering legacy code for the first time。 That will certainly make it a lot easier for them to get the job done。 。。。more
Moritz
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This is one of the best general books about programming。 The topic of refactoring applies to all programming languages and is relevant in any tech stack。 A very large portion of software development is refactoring。 Even when it is not about increasing quality or maintainability but we are creating new features， much of our time is still spend on preparatory refactoring。When creating a features in large scale software it is usually not good to change the software's behavior right away。 It is bett This is one of the best general books about programming。 The topic of refactoring applies to all programming languages and is relevant in any tech stack。 A very large portion of software development is refactoring。 Even when it is not about increasing quality or maintainability but we are creating new features， much of our time is still spend on preparatory refactoring。When creating a features in large scale software it is usually not good to change the software's behavior right away。 It is better to first adapt the structure of the software to make the features easy to implement。This book gives very good， detailed and applicable advice。 I recommend it for everyone working in software development。 。。。more
Zeljko Cavic
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The book covers lots of typical situations and describes how the code should look like。Some examples are too simple and obvious。
tyler
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really good， informative book。this definitely doesn't feel like the kind of book you "read" （even though you can）。 it's more like a catalog you skim over from time to time to remind yourself that there are other ways to do things that are maybe clearer than the way you did them。 after programming for a while， a lot of these refactorings are things that just make sense when you read them in a book， but are obviously harder to apply when you're knee deep in code。 it's also very methodical， which i really good， informative book。this definitely doesn't feel like the kind of book you "read" （even though you can）。 it's more like a catalog you skim over from time to time to remind yourself that there are other ways to do things that are maybe clearer than the way you did them。 after programming for a while， a lot of these refactorings are things that just make sense when you read them in a book， but are obviously harder to apply when you're knee deep in code。 it's also very methodical， which is helpful when you're trying to deal with particularly complex refactorings （for simpler changes， it's easy to keep all the steps in mind at once and just do them wholesale instead of following Fowler's step-by-step instructions）。undoubtedly great to have as a reference to physically flip through in times of need or boredom。 。。。more
Petar Ivanov
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It's a must-read for every software engineer or anyone involved in the programming world。 I've picked most of the ideas in this book from other places such as Clean Code， The Clean Coder and etc， but still， I learned a couple of things。Refactoring is a must-have in your toolbox。 It should be done incrementally and always think twice before you start refactoring。 Every "good practice" could be a nightmare in the end and vice versa。 Have in mind that refactoring is a continuous process！ It's a must-read for every software engineer or anyone involved in the programming world。 I've picked most of the ideas in this book from other places such as Clean Code， The Clean Coder and etc， but still， I learned a couple of things。Refactoring is a must-have in your toolbox。 It should be done incrementally and always think twice before you start refactoring。 Every "good practice" could be a nightmare in the end and vice versa。 Have in mind that refactoring is a continuous process！ 。。。more
Pratik Dayama
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Even though many of the refactoring（s） mentioned in the book are automated， the book taught me the thought process behind taking safe small steps to achieve big results。 The book was enhanced by flashbacks to the code bases I have worked on and how some of the refactoring（s） could have been done in a short amount of time but would have made the experience for everyone a whole lot smoother。 I’ll definitely be coming back to refer to the extensive catalogue of various refactoring（s） and the funny Even though many of the refactoring（s） mentioned in the book are automated， the book taught me the thought process behind taking safe small steps to achieve big results。 The book was enhanced by flashbacks to the code bases I have worked on and how some of the refactoring（s） could have been done in a short amount of time but would have made the experience for everyone a whole lot smoother。 I’ll definitely be coming back to refer to the extensive catalogue of various refactoring（s） and the funny quips。 。。。more
Fabrice
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Great insight in the mind of a great programmerThe catalogue of refactoring is interesting。 The way Martin （and also Kent Beck according to Martin） approach coding is fascinating。 The small step approach and the thinking put into every step is inspirational and the book worth reading just to understand that。
Michael Koltsov
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This year was supposed to be full of reading and learning new things， but the reality has shown that it had different plans for my time。 That's why it took me much longer that usual to finish this book and therefore I may forget some of the things that I found interesting in it。I must admit that as a writer Martin Fowler has his unique style that you start to grasp after finishing just a few pages of any of his books。 He's one of the father figures of the "make code for humans not for the machin This year was supposed to be full of reading and learning new things， but the reality has shown that it had different plans for my time。 That's why it took me much longer that usual to finish this book and therefore I may forget some of the things that I found interesting in it。I must admit that as a writer Martin Fowler has his unique style that you start to grasp after finishing just a few pages of any of his books。 He's one of the father figures of the "make code for humans not for the machines" movement that some may also call "clean code & architecture"。 It's always interesting when in his books his starts to mention his buddies who'd contributed a lot to make developer's life easier。 In this book for example I found out that "smelly code" saying was invented because Kent Beck had to fight two things simultaneously: someone's bad code as well as smelly diapers。 A quick glance to other people's lives is something that you can't often find in technical books。Speaking of the book itself I don't think that there was much to be surprised about since the first edition。 More controversial refactoring methods have been added， it always frightens me when one example contradicts with the one that you read a few pages ago。 But that's the art of writing elegant code that can pass code reviews。 You never know what type of refactoring will be useful until you try all of them。 And some of them can be opposite to one another， but that what makes good developers artists not just craftsmen。I enjoyed the choice of switching to Javascript to illustrate the refactorings。 It made the book much more concise and at the same time if JS is not your primary language it makes you think how this or that example would work in your language。 That's the right way to go in my opinion。 。。。more
Shyamsundar Parthasarathy
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Nice book with lot of practical examples that ground the theory。
Keith
，
大师之作，计算机科学领域足以放入名人堂的作品。轻松的文笔能传达通透的观点，作者对于重构概念的理解和把握让人叹服。唯一读过类似的文风的作品是《The Pragmatic Programmer: Your Journey to Mastery》，都是大师之作。这本书躺在我的书架上许久了，长期以来因为他的厚实让人望而生畏，没想到翻开后，2天地铁+午间，再加今天出差空暇的下午时间就读完了。一方面归功于作者的深入浅出的文笔，另一方面是因为，作者传达的观点，在我的编程生涯中已经从方方面面渗透进我的常识，并已经不自觉的实践过了，这一现象，不得不更让人叹服本书观点的开创性，远见性，已经长久的活力证明的正确性。更让人惊艳的是，书的末尾还从观点和软件推广的角度做了思考，对于技术传播的理论做了探讨，虽然只是寥寥数笔，但是对于我们见怪不怪的重复造轮子却不推广轮子的现象有所针指。本书不适合初学编程的读者，推荐每位有初-中级编程经验的读者开卷，你一定不会后悔。
Dhruv Bhatnagar
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Good book for new developers as well as those who have good work experience。 This book provides a sort of mental model（s） for refactoring code。 The book is well divided into small chunks and you can navigate easily and finish the book fast。
Yure Kesley
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Great book。 I'm sure that it will be very helpful for everyone that to read this book Great book。 I'm sure that it will be very helpful for everyone that to read this book 。。。more
Matthew King
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It was a good read but seemed targeted towards developers early in the career （i。e。 would be extremely beneficial if you're in college or not as exposed to the field quite yet）。 Most of the mid to later chapters were refactorings I've seen performed on the job （frequently）， but they weren't exactly "labeled"。 That said， it contains a ton of useful information and I was able to save several snippets in the book for later reference as I grow as a developer myself。 It was a good read but seemed targeted towards developers early in the career （i。e。 would be extremely beneficial if you're in college or not as exposed to the field quite yet）。 Most of the mid to later chapters were refactorings I've seen performed on the job （frequently）， but they weren't exactly "labeled"。 That said， it contains a ton of useful information and I was able to save several snippets in the book for later reference as I grow as a developer myself。 。。。more
Sepehr
，
The must-read catalog。
Suphan Fayong
，
There are 12 chapters。 The content is basic up to chapter 9 and starts interesting at chapter 10。 Most of the examples are straightforward。 Still， they are great for beginners。 A few years of coding experience is required to appreciate this book。 However， if you have a lot of coding experience and improve yourself for so long， this book might be too easy。Some of the ideas in this book are controversy， but I think it is fine since this is the nature of books about cleaning code。
هدى
，
If you don't like reading books you can scan this websitehttps://refactoring。guru/refactoringIt's the same but briefer and more orgnaized If you don't like reading books you can scan this websitehttps://refactoring。guru/refactoringIt's the same but briefer and more orgnaized 。。。more
Yury Jefse
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Gostei da estrutura do livro， de como é claro ao explicar cada técnica， e como é aplicado。 Os códigos da edição que li， que é a segunda， é escrito em Javascript já seguindo as tecnologias que estão badaladas no mercado。 Vale ressaltar que esse livro é mais indicado para iniciantes até intermediário。 Se você é avançado e espera coisas novas aqui， infelizmente você vai se frustrar; mas caso queira reforçar conceitos e técnicas de boas práticas， esse livro é bom。
Burak IŞIK
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Refactor， Compile， Test Cycle！
John Smith
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Even a little bit old already， I like the style and the examples。 They were quite helpful during my last project！ Kudos！
Gencho
，
Lots of nice tips and tricks。 Easy to read and follow！ Recommend it！
Adam Rice
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Fowler really does try to provide a generic guide for refactoring and his commitment to keeping it updated should be applauded。 Unfortunately， however， there can be quite substantial differences between languages that can render a large number of the examples not valuable in my primary language， Ruby。 I tried to re-build every example in Ruby to create a collection of relevant refactoring examples but found I was contorting myself into very unusual positions。There is an old Ruby Edition of this Fowler really does try to provide a generic guide for refactoring and his commitment to keeping it updated should be applauded。 Unfortunately， however， there can be quite substantial differences between languages that can render a large number of the examples not valuable in my primary language， Ruby。 I tried to re-build every example in Ruby to create a collection of relevant refactoring examples but found I was contorting myself into very unusual positions。There is an old Ruby Edition of this book and I think I will get more out of reading that。 。。。more
Antriksh
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Must read once for any developer， who enjoys coding ！
Daniel
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I never had the chance to read a comprehensive resource， like this book， on "code smells" and refactoring techniques to get rid of them whether in my own code or someone else's work， until now。Code smells are basically bad practices in writing any piece of code that impedes further extension， or modification of the software and increases the complexity of the code by making it harder to understand and change。Well after reading this popular classic， which has been revised recently， it immediately I never had the chance to read a comprehensive resource， like this book， on "code smells" and refactoring techniques to get rid of them whether in my own code or someone else's work， until now。Code smells are basically bad practices in writing any piece of code that impedes further extension， or modification of the software and increases the complexity of the code by making it harder to understand and change。Well after reading this popular classic， which has been revised recently， it immediately raised to the top of my list for the best books on professional coding practices。I never felt lost during reading 400 pages of technical descriptions which is a clear sign that Martin Fowler is a fantastic communicator and a great author。I can only recommend this to the software developers of all levels， because I'm sure after reading this， you will level up in your coding skills， no matter your level。 。。。more
Djamel Benali
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i follow the book principles， i become a better at clean code ， refactoring
David Stevenson
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This is a review of the 2nd edition。While I thought I had a decent knowledge of what refactoring was， having read the first 100 pages of this book， I had to admit to myself that my knowledge had been shallow at best。 People in IT do have a tendency to fling terms around loosely， and “refactoring” is one of those terms。The first part of the book sorts you out in that respect， and also gives you an education about why refactoring is important and also how to go about doing it in your software deve This is a review of the 2nd edition。While I thought I had a decent knowledge of what refactoring was， having read the first 100 pages of this book， I had to admit to myself that my knowledge had been shallow at best。 People in IT do have a tendency to fling terms around loosely， and “refactoring” is one of those terms。The first part of the book sorts you out in that respect， and also gives you an education about why refactoring is important and also how to go about doing it in your software development practice。 The first 100 pages of the book is five-star material。The remainder of the book （the canonical edition of which is the web edition now， so worth checking that out for further updates since your dead tree copy was printed） is a reference to various individual refactorings that one might frequently have to reach for。 The book itself warns you that you don’t really want to read through page by page here， but after buying a book， I am typically one to read through anyway， to feel I’m maximizing the value of my purchase。 Some of the refactorings are a little tough to get through in one sitting， but some refactorings are difficult to clearly illustrate via written prose and code snippets。 To the extent it can be done I think Martin Fowler has done a great job。 But it’s hard for me to mark such as 5 stars - it’s not something I will likely ever read through page by page again， but I am no doubt better off for having done it this first time。 。。。more
Zoe
，
This book took forever to finish！ But I did it， that too in 2020。 I think the perfect time to read this is when you have started out and are a few months/years into the tech world。 Many of the refactorings are just common sense but when thinking in terms of maintainable code are quite handy。 If nothing else， definitely recommend reading the third chapter that covers the smells of bad code。
Michael
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