Clean Code: A Handbook of Agile Software Craftsmanship, 1st edition

Published by Prentice Hall PTR (August 1, 2008) © 2009

  • Robert C. Martin



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Even bad code can function. But if code isn’t clean, it can bring a development organisation to its knees. Every year, countless hours and significant resources are lost because of poorly written code. But it doesn’t have to be that way.

Noted software expert Robert C. Martin presents a revolutionary paradigm with Clean Code: A Handbook of Agile Software Craftsmanship. Martin has teamed up with his colleagues from Object Mentor to distil their best agile practice of cleaning code “on the fly” into a book that will instil within you the values of a software craftsman and make you a better programmer—but only if you work at it.

What kind of work will you be doing? You’ll be reading code—lots of code. And you will be challenged to think about what’s right about that code, and what’s wrong with it. More importantly, you will be challenged to reassess your professional values and your commitment to your craft.

Clean Code is divided into three parts. The first describes the principles, patterns, and practices of writing clean code. The second part consists of several case studies of increasing complexity. Each case study is an exercise in cleaning up code—of transforming a code base that has some problems into one that is sound and efficient. The third part is the payoff: a single chapter containing a list of heuristics and “smells” gathered while creating the case studies. The result is a knowledge base that describes the way we think when we write, read, and clean code.

Readers will come away from this book understanding

  • How to tell the difference between good and bad code
  • How to write good code and how to transform bad code into good code
  • How to create good names, good functions, good objects, and good classes
  • How to format code for maximum readability
  • How to implement complete error handling without obscuring code logic
  • How to unit test and practice test-driven development
Foreword                      xix
Introduction              xxv
On the Cover                     xxix

Chapter 1: Clean Code                    1
There Will Be Code                        2
Bad Code                           3
The Total Cost of Owning a Mess                 4
Schools of Thought                        12
We Are Authors                      13
The Boy Scout Rule                     14
Prequel and Principles                   15
Conclusion                        15
Bibliography                  15

Chapter 2: Meaningful Names                     17
Introduction               17
Use Intention-Revealing Names                     18
Avoid Disinformation                         19
Make Meaningful Distinctions                20
Use Pronounceable Names                            21
Use Searchable Names                                22
Avoid Encodings                          23
Avoid Mental Mapping                    25
Class Names                    25
Method Names                              25
Don’t Be Cute                    26
Pick One Word per Concept                 26
Don’t Pun                    26
Use Solution Domain Names                    27
Use Problem Domain Names                   27
Add Meaningful Context                       27
Don’t Add Gratuitous Context                    29
Final Words                        30

Chapter 3: Functions                                           31
Small!                               34
Do One Thing                         35
One Level of Abstraction per Function                           36
Switch Statements                     37
Use Descriptive Names                      39
Function Arguments                          40
Have No Side Effects                          44
Command Query Separation                           45
Prefer Exceptions to Returning Error Codes              46
Don’t Repeat Yourself                          48
Structured Programming                   48
How Do You Write Functions Like This?                49
Conclusion                          49
SetupTeardownIncluder                        50
Bibliography                                       52

Chapter 4: Comments                                                  53
Comments Do Not Make Up for Bad Code                   55
Explain Yourself in Code                        55
Good Comments                              55
Bad Comments                          59
Bibliography                          74

Chapter 5: Formatting                                           75
The Purpose of Formatting                     76
Vertical Formatting                         76
Horizontal Formatting                         85
Team Rules                      90
Uncle Bob’s Formatting Rules                  90
Chapter 6: Objects and Data Structures                      93
Data Abstraction                     93
Data/Object Anti-Symmetry                        95
The Law of Demeter                         97
Data Transfer Objects                     100
Conclusion                       101
Bibliography                           101

Chapter 7: Error Handling                           103
Use Exceptions Rather Than Return Codes                  104
Write Your Try-Catch-Finally Statement First                    105
Use Unchecked Exceptions                         106
Provide Context with Exceptions                      107
Define Exception Classes in Terms of a Caller’s Needs                107
Define the Normal Flow                  109
Don’t Return Null                        110
Don’t Pass Null                       111
Conclusion                           112
Bibliography                                 112

Chapter 8: Boundaries                                                            113
Using Third-Party Code                               114
Exploring and Learning Boundaries                      116
Learning log4j                         116
Learning Tests Are Better Than Free                      118
Using Code That Does Not Yet Exist                     118
Clean Boundaries                           120
Bibliography                           120

Chapter 9: Unit Tests                                    121
The Three Laws of TDD                   122
Keeping Tests Clean                          123
Clean Tests                        124
One Assert per Test                        130
F.I.R.S.T.                      132
Conclusion                       133
Bibliography                        133

Chapter 10: Classes                         135
Class Organization                  136
Classes Should Be Small!                 136
Organizing for Change                   147
Bibliography                     151

Chapter 11: Systems                                                  153
How Would You Build a City?                     154
Separate Constructing a System from Using It                      154
Scaling Up                            157
Java Proxies                        161
Pure Java AOP Frameworks                     163
AspectJ Aspects                     166
Test Drive the System Architecture                      166
Optimize Decision Making                       167
Use Standards Wisely, When They Add Demonstrable Value                168
Systems Need Domain-Specific Languages                   168
Conclusion                    169
Bibliography                      169

Chapter 12: Emergence                        171
Getting Clean via Emergent Design                171
Simple Design Rule 1: Runs All the Tests                  172
Simple Design Rules 2–4: Refactoring                        172
No Duplication                      173
Expressive                        175
Minimal Classes and Methods               176
Conclusion                   176
Bibliography                     176

Chapter 13: Concurrency                         177
Why Concurrency?                    178
Challenges                        180
Concurrency Defense Principles                   180
Know Your Library                    182
Know Your Execution Models                       183
Beware Dependencies Between Synchronized Methods            185
Keep Synchronized Sections Small                  185
Writing Correct Shut-Down Code Is Hard                 186
Testing Threaded Code                     186
Conclusion                      190
Bibliography                         191

Chapter 14: Successive Refinement                     193
Args Implementation                          194
Args: The Rough Draft                       201
String Arguments                   214
Conclusion                       250

Chapter 15: JUnit Internals                                    251
The JUnit Framework                    252
Conclusion                 265

Chapter 16: Refactoring SerialDate                         267
First, Make It Work                     268
Then Make It Right                    270
Conclusion                      284
Bibliography                     284

Chapter 17: Smells and Heuristics                         285
Comments                           286
Environment                       287
Functions                            288
General                               288
Java                                     307
Names                                 309
Tests                                    313
Conclusion                         314
Bibliography                      315

Appendix A: Concurrency II                              317
Client/Server Example                           317
Possible Paths of Execution                    321
Knowing Your Library                      326
Dependencies Between Methods Can Break Concurrent Code         329
Increasing Throughput                  333
Deadlock                    335
Testing Multithreaded Code                   339
Tool Support for Testing Thread-Based Code                    342
Conclusion                    342
Tutorial: Full Code Examples                    343

Appendix B:                             349

Appendix C: Cross References of Heuristics                  409

Epilogue                           411
Index                                  413

Robert C. “Uncle Bob” Martin has been a software professional since 1970 and an international software consultant since 1990. He is founder and president of Object Mentor, Inc., a team of experienced consultants who mentor their clients worldwide in the fields of C++, Java, C#, Ruby, OO, Design Patterns, UML, Agile Methodologies, and eXtreme programming.

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