Implementation Patterns (Paperback)

Kent Beck




“Kent is a master at creating code that communicates well, is easy to understand, and is a pleasure to read. Every chapter of this book contains excellent explanations and insights into the smaller but important decisions we continuously have to make when creating quality code and classes.”

Erich Gamma, IBM Distinguished Engineer


“Many teams have a master developer who makes a rapid stream of good decisions all day long. Their code is easy to understand, quick to modify, and feels safe and comfortable to work with. If you ask how they thought to write something the way they did, they always have a good reason. This book will help you become the master developer on your team. The breadth and depth of topics will engage veteran programmers, who will pick up new tricks and improve on old habits, while the clarity makes it accessible to even novice developers.”

Russ Rufer, Silicon Valley Patterns Group


“Many people don’t realize how readable code can be and how valuable that readability is. Kent has taught me so much, I’m glad this book gives everyone the chance to learn from him.”

Martin Fowler, chief scientist, ThoughtWorks


“Code should be worth reading, not just by the compiler, but by humans. Kent Beck distilled his experience into a cohesive collection of implementation patterns. These nuggets of advice will make your code truly worth reading.”

Gregor Hohpe, author of Enterprise Integration Patterns


“In this book Kent Beck shows how writing clear and readable code follows from the application of simple principles. Implementation Patterns will help developers write intention revealing code that is both easy to understand and flexible towards future extensions. A must read for developers who are serious about their code.”

Sven Gorts


Implementation Patterns bridges the gap between design and coding. Beck introduces a new way of thinking about programming by basing his discussion on values and principles.”

Diomidis Spinellis, author of Code Reading and Code Quality


Software Expert Kent Beck Presents a Catalog of Patterns Infinitely Useful for Everyday Programming


Great code doesn’t just function: it clearly and consistently communicates your intentions, allowing other programmers to understand your code, rely on it, and modify it with confidence. But great code doesn’t just happen. It is the outcome of hundreds of small but critical decisions programmers make every single day. Now, legendary software innovator Kent Beck–known worldwide for creating Extreme Programming and pioneering software patterns and test-driven development–focuses on these critical decisions, unearthing powerful “implementation patterns” for writing programs that are simpler, clearer, better organized, and more cost effective.


Beck collects 77 patterns for handling everyday programming tasks and writing more readable code. This new collection of patterns addresses many aspects of development, including class, state, behavior, method, collections, frameworks, and more. He uses diagrams, stories, examples, and essays to engage the reader as he illuminates the patterns. You’ll find proven solutions for handling everything from naming variables to checking exceptions.


This book covers

  • The value of communicating through code and the philosophy behind patterns
  • How and when to create classes, and how classes encode logic
  • Best practices for storing and retrieving state
  • Behavior: patterns for representing logic, including alternative paths
  • Writing, naming, and decomposing methods
  • Choosing and using collections
  • Implementation pattern variations for use in building frameworks

Implementation Patterns will help programmers at all experience levels, especially those who have benefited from software patterns or agile methods. It will also be an indispensable resource for development teams seeking to work together more efficiently and build more maintainable software. No other programming book will touch your day-to-day work more often.

Table of Contents

Preface  xv

Chapter 1: Introduction  1

Tour Guide  3

And Now...  4

Chapter 2: Patterns  5

Chapter 3: A Theory of Programming  9

Values  10

Principles  13

Conclusion  18

Chapter 4: Motivation  19

Chapter 5: Class  21

Class  22

Simple Superclass Name  23

Qualified Subclass Name  24

Abstract Interface   24

Interface  26

Abstract Class  26

Versioned Interface  27

Value Object  28

Specialization  31

Subclass  32

Implementor  34

Inner Class  34

Instance-Specific Behavior  36

Conditional  36

Delegation  38

Pluggable Selector  40

Anonymous Inner Class  41

Library Class  41

Conclusion  42

Chapter 6: State  43

State  44

Access  45

Direct Access  46

Indirect Access  47

Common State  47

Variable State  48

Extrinsic State  50

Variable  50

Local Variable  51

Field  52

Parameter  53

Collecting Parameter  55

Optional Parameter  56

Var Args  56

Parameter Object  57

Constant  58

Role-Suggesting Name  58

Declared Type  60

Initialization  61

Eager Initialization  61

Lazy Initialization  62

Conclusion  62

Chapter 7: Behavior  63

Control Flow  64

Main Flow  64

Message  65

Choosing Message  65

Double Dispatch  66

Decomposing (Sequencing) Message  67

Reversing Message  67

Inviting Message  68

Explaining Message  69

Exceptional Flow  70

Guard Clause  70

Exception  72

Checked Exceptions  72

Exception Propagation  73

Conclusion  73

Chapter 8: Methods  75

Composed Method  77

Intention-Revealing Name  79

Method Visibility  80

Method Object  82

Overridden Method  83

Overloaded Method  83

Method Return Type  84

Method Comment  85

Helper Method  85

Debug Print Method  86

Conversion  87

Conversion Method  87

Conversion Constructor  88

Creation  88

Complete Constructor  89

Factory Method  90

Internal Factory  91

Collection Accessor Method  91

Boolean Setting Method  93

Query Method  93

Equality Method  94

Getting Method  95

Setting Method  96

Safe Copy  97

Conclusion  98

Chapter 9: Collections  99

Metaphors  100

Issues  101

Interfaces  103

Implementations  107

Collections  110

Extending Collections  114

Conclusion  115

Chapter 10: Evolving Frameworks  117

Changing Frameworks without Changing Applications  117

Incompatible Upgrades  118

Encouraging Compatible Change  120

Conclusion  129

Appendix A: Performance Measurement  131

Example  131

API  132

Implementation  133

MethodTimer  134

Canceling Overhead  136

Tests  136

Conclusion  142

Bibliography  145

General Programming  145

Philosophy  147

Java  148

Index  149





「代碼應該值得閱讀,不僅僅是編譯器,還有人類。肯特·貝克(Kent Beck)將他的經驗融入了一個有條理的實現模式集合中。這些寶貴的建議將使您的代碼真正值得閱讀。」

「在這本書中,肯特·貝克(Kent Beck)展示了如何從清晰易讀的代碼中獲益,這是從他的經驗中提煉出來的。」