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Essential Skills for the Agile Developer: Avoid Over- and Under-Design
Table of Contents
Series Foreword xvii
Preface xxi
Acknowledgments xxiii
About the Authors xxv
Part I: The Core Trim Tabs 1
Chapter 1: Programming by Intention 3
Programming by Intention: A Demonstration 3
Advantages 6
Summary 18
Chapter 2: Separate Use from Construction 21
An Important Question to Ask 21
Perspectives 22
Timing Your Decisions 30
Overloading and C++ 31
Validating This for Yourself 32
Summary 33
Chapter 3: Define Tests Up Front 35
A Trim Tab: Testing and Testability 35
What Is Testing? 35
Testability and Code Quality 36
Case Study: Testability 37
A Reflection on Up-Front Testing 39
Summary 44
Chapter 4: Shalloway’s Law and Shalloway’s Principle 45
Types of Redundancy 46
Redefining Redundancy 46
Other Types of Redundancy 47
The Role of Design Patterns in Reducing Redundancy 48
Few Developers Spend a Lot of Time Fixing Bugs 48
Redundancy and Other Code Qualities 50
Summary 52
Chapter 5: Encapsulate That! 53
Unencapsulated Code: The Sabotage of the Global Variable 53
Encapsulation of Member Identity 54
Self-Encapsulating Members 56
Preventing Changes 58
The Difficulty of Encapsulating Reference Objects 59
Breaking Encapsulation with Get() 62
Encapsulation of Object Type 64
Encapsulation of Design 67
Encapsulation on All Levels 69
Practical Advice: Encapsulate Your Impediments 69
Summary 72
Chapter 6: Interface-Oriented Design 75
Design to Interfaces 75
Definition of Interface 75
Interface Contracts 76
Separating Perspectives 77
Mock Implementations of Interfaces 79
Keep Interfaces Simple 79
Avoids Premature Hierarchies 80
Interfaces and Abstract Classes 81
Dependency Inversion Principle 82
Polymorphism in General 83
Not for Every Class 84
Summary 84
Chapter 7: Acceptance Test—Driven Development (ATDD) 85
Two Flows for Development 85
Acceptance Tests 88
An Example Test 88
Implementing the Acceptance Tests 90
An Exercise 95
What to Do If the Customer Won’t Tell You 95
Summary 96
Part II: General Attitudes 97
Chapter 8: Avoid Over- and Under-Design 99
A Mantra for Development 99
The Pathologies of Code Qualities 100
Avoid Over- and Under-Design 101
Minimize Complexity and Rework 102
Never Make Your Code Worse/Only Degrade Your Code Intentionally 102
Keep Your Code Easy to Change, Robust, and Safe to Change 103
A Strategy for Writing Modifiable Code in a Non-Object-Oriented or Legacy System 103
Summary 107
Chapter 9: Continuous Integration 109
Branching the Source Code 109
The Merge-Back 115
Test-Driven Development and Merge Cost 117
Continuous Integration 119
Continuous Integration Servers 121
Summary 122
Part III: Design Issues 125
Chapter 10: Commonality and Variability Analysis 127
Using Nouns and Verbs as a Guide: Warning, Danger Ahead! 127
What Is the Real Problem? 130
What We Need to Know 131
Commonality and Variability Analysis 132
A New Paradigm for Finding Objects 134
The Analysis Matrix: A Case Study 136
Summary 145
Chapter 11: Refactor to the Open-Closed 147
The Open-Closed Principle 147
Refactoring 154
Summary 161
Chapter 12: Needs versus Capabilities Interfaces 163
The Law of Demeter 163
Coupling, Damned Coupling, and Dependencies 166
The Ideal Separation: Needs Interfaces and Capabilities Interfaces 168
Back to the Law of Demeter 169
Summary 171
Chapter 13: When and How to Use Inheritance 173
The Gang of Four 173
Initial Vectors, Eventual Results 176
Favoring Delegation 178
The Use of Inheritance versus Delegation 180
Uses of Inheritance 181
Scalability 183
Applying the Lessons from the Gang of Four to Agile Development 184
Testing Issues 185
There’s More 187
Part IV: Appendixes 189
Appendix A: Overview of the Unified Modeling Language (UML) 191
What Is the UML? 191
The Class Diagram 192
Sequence Diagram 198
Summary 200
Appendix B: Code Qualities 201
Christmas-Tree Lights: An Analogy 201
Cohesion 204
Coupling 205
Redundancy 207
Encapsulation 208
Appendix C: Encapsulating Primitives 211
Encapsulating Primitives in Abstract Data Types 211
Principles 212
Narrow the Contract 213
Expanding Abstract Data Types 214
Use Text as External Values 215
Enumerations Instead of Magic Values 217
Disadvantages 218
Summary 219
Index 221
