Product Description
As the application of object technology-particularly the Java programming language-has become commonplace, a new problem has emerged to confront the software development community. Significant numbers of poorly designed programs have been created by less-experienced developers, resulting in applications that are inefficient and hard to maintain and extend. Increasingly, software system professionals are discovering just how difficult it is to work with these inherit… More >>
Refactoring: Improving the Design of Existing Code
Like the Gang of Four’s landmark book _Design Patterns_, Fowler and his cohorts have created another catalog-style book, this time on refactoring.
Refactoring refers to taking existing, working software, and changing it about to improve its design, so that future modifications and enhancements are easier to add. _Refactoring_ is primarily a catalog of 70 or so different kinds of improvements you can make to object-oriented software.
Each entry in the catalog describes an implementation problem, the solution, motivation for applying the solution, the mechanics of the refactoring, and examples. The book’s examples are all in Java, but C++ programmers should be able to approach the refactorings with ease. Often, Fowler diagrams the refactorings in UML, so a little Unified Modeling Language experience will help, too.
While the catalog is nice, the kinds of refactorings are obvious is most cases. Even moderately experienced programmers won’t need the step-by-step mechanics described. The real benefit, though, is that the mechanics of each refactoring help guarantee that you can pull off the refactoring without introducing new bugs or side effects. They encourage you to take smaller, verifiable steps, than the more gross refactorings that most developers would naturally take. You actually save time doing so.
How do you know your refactorings are safe? Unit testing is the answer that Fowler et al. provide. Java developers will find the introduction to the Junit Testing Framework the most valuable part of the book, more so than the catalog of refactorings itself.
There’s more to the book than the catalog and Junit, of course. There’s discussion of the history of refactoring, how to evaluate refactoring tools, and how to convince management that what appears to be an overhead activity is actually useful in the long run.
Unfortunately, these sections are all too brief. And there is no discussion of how refactoring fits in with various software development processes. For example, programmers using Extreme Programming (XP) would probably feel right at home with Fowler’s recommendations of refactoring in duets and unit testing, but developers stuck with a Software Engineering Institute process like PSP categorize testing as failure time and something to be minimized if not avoided. Cleanroom developers are taught that unit testing inteferes with metrics for quality, and that verifications are what should be done. Should such developers redo verifications after each refactoring? There’s no answer in this book.
An unusual chapter, called “Bad Smells in Code,” gives overall motivation for the refactorings. These vague notions, such as “long methods” or “lazy classes” humorously provide a foundation for starting your own refactorings. I say “humorously” because (mostly) Beck’s and Fowler’s odd analogies (classes becoming too intimate and delving in each others’ private parts) provoke a chuckle (as if a chapter about “bad smells” in code weren’t enough).
Overall, I’ve enjoyed reading this book and referring to the catalog while putting my own unit tests and refactorings into practice. Fowler’s writing style is smooth and fluid, and it’s easy to digest the catalog in no time. The book’s typesetting is crisp, the figures quite clean, and both the refactoring index and “smell” index are enormously useful.
Rating: 4 / 5
A little while back I was introduced to a word I had never heard before, Refactoring. I was told to
get Martin Fowler’s book and read it so I could gain a better understanding of what Refactoring
was. Well folks, I would classify this book as a ‘Hidden Treasure’.
Although it is not a flashy or well known title, I believe its impact can be much deeper and long
lasting than many of the mainstream, more popular technology books. The underlying theories
that it teaches can be applied for years, even when languages change.
There are only a couple of things I would change about this book, which I will mention below.
Preface
The Preface it brief enough, and gives the definition for the word Refactoring. This is a good thing
because right form the start you get the true definition of Refactoring. In short, refactoring is the
process of changing code to improve the internal structure, but not changing the external
behavior.
Chapter 1: Refactoring, a First Example
In this chapter Mr. Fowler tries to start by showing a simple Refactoring example. The problem is
that the chapter then goes on for 50+ pages. Mr. Fowler explains his reasons for doing this, but I
think that a simple example should have been much simpler. Especially when it is in the first
chapter of the book. It’s not that this isn’t a good chapter. I feel it’s just too soon in the book. I
would have put it at the end.
Chapter 2: Principles of Refactoring
This is an excellent chapter. The definition of Refactoring is discussed as well as the following
questions: Why should you refactor? When should you refactor? What do I tell my manager? This
last question may seem funny, but when you read this chapter you will understand why it is in
there. This chapter also discusses common problems that occur during Refactoring, and
Refactoring and performance.
Chapter 3: Bad Smells in Code
In this chapter things that cause code to ‘smell’ are discussed. When code ‘smells’ it could be an
indicator that refactoring is needed. 22 different ‘smells’ are discussed. My favorites were
Duplicated Code, Large Class, and Lazy Class. This is a chapter full of awesome hints.
Chapter 4: Building Tests
Building tests is an important part refactoring. Refactoring is done in small steps, and after every
step you should test. In this chapter the discussion covers the processes and methodology of
applying tests during refactoring.
Chapter 5: Toward a Catalog of Refactorings
This chapter is a quick setup for chapters 6 to 12. Mr. Fowler explains his method for cataloging
the individual refactorings. What is pretty amazing is that he has taken a lot of time naming and
detailing each refactoring.
Chapter 6: Composing Methods
One of my favorite chapters. Mr. Fowler opens by saying, “A large part of my refactoring is
composing methods to package code properly.” This chapter is all about that. 9 total refactorings
are explained. My favorite ones are Inline Method and Extract Method.
Chapter 7: Moving Features Between Objects
Sometimes you need to move things from one object to another. This chapter discusses the art of
moving features between objects. 8 total refactorings are discussed and detailed. My favorite
from this chapter is Extract Class.
Chapter 8: Organizing Data
A very large chapter that discusses in meticulous detail 16 refactorings that will make it much
easier to work with data. One thing that becomes very obvious in this chapter is that certain
refactorings can go either way. What I mean is illustrated by these two: Change Value to
Reference and Change Reference to Value. So some refactorings are not just one way deals. It
just depends on the situation.
Chapter 9: Simplifying Conditional Expressions
This is a very useful chapter since conditional logic is a common occurrence in the programming
world. Because conditional logic has a tendency to get very complex, this chapter has 8
refactorings that will help you simplify things.
Chapter 10: Making Method Calls Simpler
The 15 refactorings in this chapter help teach us how to make method calls easier to deal with.
They range from the very simple Rename Method to the more complex Replace Constructor with
Factory Method.
Chapter 11: Dealing with Generalization
Here are 12 refactorings dealing with the situations that arise from generalization. Inheritance,
Delegation, and Interfaces are some of the topics discussed.
Chapter 12: Big Refactorings
Kent Beck co-wrote this chapter with Mr. Fowler. They discuss what they call the 4 Big
Refactorings: Tease Apart Inheritance, Convert Procedural Design to Objects, Separate Domain
from Presentation, and Extract Hierarchy. These refactorings are of a more all-encompassing
type than the smaller individual refactorings from the preceding chapters. The co-authors do a
great job at putting in a nutshell what would normally take very long explanations.
Chapter 13: Refactoring, Reuse, and Reality
William Opdyke writes this chapter. He discusses his experiences with refactoring as well as
other subjects like why developers are reluctant to refactor and reducing the overhead of
refactoring. This chapter is an excellent ‘putting it all together’ chapter, and really helps put into
perspective the ideas that the book teaches.
Chapter 14: Refactoring Tools
Don Roberts and John Brant co-author this chapter. They discuss, as the chapter title would
indicate, refactoring tools.
Chapter 15: Putting It All Together
Kent Beck gives a quick 4-page wrap up.
One other thing I would change about the book is that I would want there to be examples in other
languages besides Java. I have practically no Java skills. For me the book would have been an
easier and faster read if it would have had examples in VB.net. Fortunately I understand enough
to get the idea of what is being taught, and that is the most important point.
Well as I said above, this book is really what I would consider a ‘hidden treasure’. The things
discussed will help many people write better, more understandable code for years to come. I
would give it a 9.5 out of 10. It is well worth the {price}
Rating: 5 / 5
One can read good books on a specific technology (COM, UML etc) or on specific programming languages or even on different approaches to software development (RUP, OPEN etc) but every now and then a true classic comes along. Like Design Patterns 4 years ago now refactoring comes along. Every serious OO developer should own both of these books. Get your hands on Refactoring if only to read chapter 3, which summarises all the ‘bad smells’ that may creep into code. 21 generic examples of what is bad programming and why. The remainder of the book describes numerous techniques (refactorings) for changing existing code in order to remove the ‘smell’. Most refactorings are accompanied with some UML, which should be enough to get the idea, and they are then further described in Java. What makes this great a book is that it can be used as a reference very easily since its design was well thought out for this purpose with a comprehensive index and tables matching smells and respective refactorings. If any of this rings a bell to CODE COMPLETE readers it should cause the ideas are very similar but very much updated here. Fowler’s writing style makes once again for easy, pleasant reading. Unreservedly recommended.
Rating: 5 / 5
I’ve known about this book for over a year. Initially, I thought it was about re-engineering legacy systems. I don’t do that, so I didn’t give it much thought. Over the past year, I have stumbled across repeated references to this book. Everyone seems to cite it, and now I understand why.
It’s very easy to fall into ‘analysis paralysis’ when doing object design. A commonly heard complaint is “I have created 27 different class diagrams, and 42 separate sequence diagrams, but I can’t seem to get any code written…” XP’s popularity is due, in part, becuase it get’s you into action–you begin writing code immediately, instead of creating diagrams for weeks (or months) on end. XP’s motto could be “just do it!”
But how does one reconcile this “code first, ask questions later” mentality with an acknowledged need to at least do some design work? In “Refactoring”, Martin Fowler provides the answer. His prescription is to create some code to get something working, then look at the code to see how it might be improved– refactor it.
In Fowler’s view, you won’t really understand the problem until you have coded it, so instead of spending the next three weeks trying to find the perfect pattern for your next task, forget the pattern, and get some code going. Once you’ve got something workable, then think about patterns you might back into from your existing code.
Of course, that’s a gross oversimplification of the process, but it gives a flavor of the ready-fire-aim process that ‘Refactoring’ is built around. And it seems to work–even people who don’t buy into other core practices of XP seem to have adopted refactoring as a central element in their process.
The catalog of refactorings that the books provides are a first class reference on how to clean up particular problems. But to me, the most valuable part of the book is its first fifty pages.
Fowler starts the book with a simple, but ugly, example, that he proceeds to refactor, step-by-step, into something rather elegant. If you like to learn principles first, you might want to read the second chapter before going through the example, but I found it a very valuable exercise. I recommend coding the example in your language of choice, then refactoring along with Fowler as you work through the example.
There is a temptation to relegate refactoring, like testing, to simply another development technique. But like testing, refactoring is at the core of a development philosophy: “I know I’m not going to get it right on my first pass, so I’ll be satisfied with making it as right as I can. Having done that, I’ll have a much better idea how to make it better, and I will. But time’s a’ wasting, so I need to get moving.”
This philosophy of continuous improvement allows the developer to get into action fairly quickly, and it reduces the risk of failure-by-delay. Fowler’s book is a top-notch resource that will help the developer create more flexible code more quickly. I can recommend ‘Refactoring’ without reservation.
Rating: 5 / 5
I spent seven years in the Smalltalk environment figuring (parts) of this stuff out for myself. You don’t have to – buy Martin’s book and shave at least a few years off the learning curve.
Refactoring is an indispensable part of software development. Like it or not, whatever you write today will be “wrong” sometime in the future. You need to have techniques for transitioning to the “right” stuff. Refactoring provides you with a wealth of small tools that can make the transition easier.
Not only that, having confidence that you can refactor your code later (supported by relentless testing) actually relieves some of the pressure you feel when you write the code the first time. Get it working, then get it right. Don’t panic. Don’t sweat. Enjoy your work like you did when you started (remember?). Let Refactoring guide the way.
A practical guide for any OO developer, no matter what language you are working in, though you need enough familiarity with Java to read the examples.
Rating: 5 / 5