Implementation Patterns

"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.

Preface		xv
Acknowledgments		xvi
Introduction		1	(4)
Tour Guide		3	(1)
And Now		4	(1)
Patterns		5	(4)
A Theory of Programming		9	(10)
Values		10	(3)
Communication		10	(1)
Simplicity		11	(1)
Flexibility		12	(1)
Principles		13	(5)
Local Consequences		13	(1)
Minimize Repetition		14	(1)
Logic and Data Together		14	(1)
Symmetry		15	(1)
Declarative Expression		16	(1)
Rate of Change		17	(1)
Conclusion		18	(1)
Motivation		19	(2)
Class		21	(22)
Class		22	(1)
Simple Superclass Name		23	(1)
Qualified Subclass Name		24	(1)
Abstract Interface		24	(2)
Interface		26	(1)
Abstract Class		26	(1)
Versioned Interface		27	(1)
Value Object		28	(3)
Specialization		31	(1)
Subclass		32	(2)
Implementor		34	(1)
Inner Class		34	(2)
Instance-Specific Behavior		36	(1)
Conditional		36	(2)
Delegation		38	(2)
Pluggable Selector		40	(1)
Anonymous Inner Class		41	(1)
Library Class		41	(1)
Conclusion		42	(1)
State		43	(20)
State		44	(1)
Access		45	(1)
Direct Access		46	(1)
Indirect Access		47	(1)
Common State		47	(1)
Variable State		48	(2)
Extrinsic State		50	(1)
Variable		50	(1)
Local Variable		51	(1)
Field		52	(1)
Parameter		53	(2)
Collecting Parameter		55	(1)
Optional Parameter		56	(1)
Var Args		56	(1)
Parameter Object		57	(1)
Constant		58	(1)
Role-Suggesting Name		58	(2)
Declared Type		60	(1)
Initialization		61	(1)
Eager Initialization		61	(1)
Lazy Initialization		62	(1)
Conclusion		62	(1)
Behavior		63	(12)
Control Flow		64	(1)
Main Flow		64	(1)
Message		65	(1)
Choosing Message		65	(1)
Double Dispatch		66	(1)
Decomposing (Sequencing) Message		67	(1)
Reversing Message		67	(1)
Inviting Message		68	(1)
Explaining Message		69	(1)
Exceptional Flow		70	(1)
Guard Clause		70	(2)
Exception		72	(1)
Checked Exceptions		72	(1)
Exception Propagation		73	(1)
Conclusion		73	(2)
Methods		75	(24)
Composed Method		77	(2)
Intention-Revealing Name		79	(1)
Method Visibility		80	(2)
Method Object		82	(1)
Overridden Method		83	(1)
Overloaded Method		83	(1)
Method Return Type		84	(1)
Method Comment		85	(1)
Helper Method		85	(1)
Debug Print Method		86	(1)
Conversion		87	(1)
Conversion Method		87	(1)
Conversion Constructor		88	(1)
Creation		88	(1)
Complete Constructor		89	(1)
Factory Method		90	(1)
Internal Factory		91	(1)
Collection Accessor Method		91	(2)
Boolean Setting Method		93	(1)
Query Method		93	(1)
Equality Method		94	(1)
Getting Method		95	(1)
Setting Method		96	(1)
Safe Copy		97	(1)
Conclusion		98	(1)
Collections		99	(18)
Metaphors		100	(1)
Issues		101	(2)
Interfaces		103	(4)
Array		103	(1)
Iterable		104	(1)
Collection		104	(1)
List		104	(1)
Set		105	(1)
SortedSet		105	(1)
Map		106	(1)
Implementations		107	(3)
Collection		108	(1)
List		108	(1)
Set		108	(1)
Map		109	(1)
Collections		110	(4)
Searching		111	(1)
Sorting		112	(1)
Unmodifiable Collections		113	(1)
Single-Element Collections		114	(1)
Empty Collections		114	(1)
Extending Collections		114	(1)
Conclusion		115	(2)
Evolving Frameworks		117	(14)
Changing Frameworks without Changing Applications		117	(1)
Incompatible Upgrades		118	(2)
Encouraging Compatible Change		120	(9)
Library Class		121	(1)
Objects		121	(8)
Conclusion		129	(2)
Appendix A: Performance Measurement		131	(14)
Example		131	(1)
API		132	(1)
Implementation		133	(1)
MethodTimer		134	(2)
Canceling Overhead		136	(1)
Tests		136	(6)
Comparing Collections		137	(2)
Comparing ArrayList and LinkedList		139	(1)
Comparing Sets		140	(1)
Comparing Maps		141	(1)
Conclusion		142	(3)
Bibliography		145	(4)
General Programming		145	(2)
Philosophy		147	(1)
Java		148	(1)
Index		149

Kent Beck, one of the software industry's most creative and acclaimed leaders, consistently challenges software engineering dogma and promotes ideas like patterns, test-driven development, and Extreme Programming. Currently affiliated with Three Rivers Institute and Agitar Software, he is the author of many Addison-Wesley titles, including Test-Driven Development (2003) and, with Cynthia Andres, Extreme Programming Explained, Second Edition (2005).

Programmers make hundreds of decisions a day. Occasionally they make large-scale decisions like those covered by Design Patterns. Far more frequently they make small-scale decisions--choosing names, organizing code logically, dividing programs into coherent parts. The cumulative effect of these hour-by-hour, minute-by-minute decisions is as significant as the effect of the design decisions in making code clear, flexible, and robust. This book is a catalog of the frequent decisions programmers make and the approaches to these decisions that result in code that communicates clearly. Programmers applying Implementation Patterns achieve code that is consistent, easy to read, and easy to modify. It sets out the "bag of tricks" common to excellent programmers in Java and similar languages. Implementation Patterns will appeal to programmers wishing to improve their individual practice, teams finding a common style, and language designers looking for abstractions to add to the next generation of programming languages. The days development teams are bigger, more spread out, and frequently forced to work with legacy applications. Now more than ever clear, communicative code is essential.