Refactoring To Patterns

version 0.15

 

Joshua Kerievsky

joshua@industriallogic.com

Industrial Logic, Inc.

http://industriallogic.com

 

Table of Contents

Introduction ................... 6

Chain Constructors............................................................................................................ 12

Motivation ............ 13

Mechanics............ 13

Example ................ 13

Chaining To An Init Method ......................................................................................................... 14

Replace Multiple Constructors with Creation Methods....... 15

Motivation ............ 15

Mechanics............ 16

Example ................ 17

Parameterized Creation Methods .............................................................................................. 19

Encapsulate Classes with Creation Methods..................................... 21

Motivation ............ 22

Forces.................... 23

Mechanics............ 23

Example ................ 23

Encapsulating Inner Classes....................................................................................................... 25

Extract Creation Class................................................................................................... 27

Motivation ............ 27

Mechanics............ 28

Example ................ 28

Move Object Composition to Creation Method............................... 31

Motivation ............ 31

Prerequisites....... 31

Mechanics............ 31

Example ................ 31

Replace Multiple Instances with Singleton.......................................... 32

Replace Singleton with Object Reference.............................................. 33

Motivation ............ 33

Replace Singleton with Registry ........................................................................34

Introduce Polymorphic Creation with Factory Method......36

Motivation ............ 37

Forces.................... 37

Mechanics............ 37

Example ................ 38

Duplication Across Subclasses ................................................................................................. 40

Defer Slow Creation with Virtual Proxy................................................. 42

Motivation ............ 43

Mechanics............ 43

Example ................ 43

Replace Conditional Calculations with Strategy ..........................44

Motivation ............ 45

Mechanics............ 45

Example ................ 46

Replace Implicit Tree with Composite........................................................ 53

Motivation ............ 53

Mechanics............ 54

Example ................ 54

Encapsulate Composite with Builder ......................................................... 57

Motivation ............ 57

Mechanics............ 58

Example ................ 58

Extended Example ........................................................................................................................... 60

Extract Special-Case Behavior into Decorators............................ 63

Motivation ............ 64

Mechanics............ 65

Example ................ 65

Collections.synchronizedMap..................................................................................................... 71

Replace Hard-Coded Notifications with Observer...................... 73

Motivation ............ 74

Mechanics............ 75

Example ................ 75

Move Accumulation to Collecting Parameter ................................. 78

Motivation ............ 78

Mechanics............ 79

Example ................ 79

JUnit’s Collecting Parameter....................................................................................................... 82

Replace One/Many Distinctions with Composite......................... 83

Motivation ............ 84

Mechanics............ 84

Example ................ 85

Compose Method................................................................................................................... 86

Motivation ............ 86

Mechanics............ 87

Example 1............. 88

Example 2............. 91

Example 3............. 97

Separate Versions with Adapters ......................................................................99

Motivation .......... 100

Mechanics.......... 100

Example .............. 101

Adapting with Annonymous Inner Classes......................................................................... 106

Adapting Legacy Systems.......................................................................................................... 106

Adapt Interface...................................................................................................................... 107

Motivation .......... 107

Mechanics.......... 108

Example .............. 108

Replace Type with Type-Safe Enum........................................................... 110

Motivation .......... 111

Mechanics.......... 112

Example .............. 112

Replace State-Altering Conditionals with State........................... 118

Motivation .......... 119

Mechanics.......... 120

Example .............. 121

Replace Singleton with Constant.................................................................... 132

Motivation .......... 132

Mechanics.......... 132

Example .............. 132

Replace Retrieval with Listener........................................................................ 133

Motivation .......... 133

Mechanics.......... 133

Example .............. 133

References .................. 134

Appendix A – Naming Conventions .......................................................................................................... 135

Appendix B – Loan Terminology .............................................................................................................. 136

Conclusion ................. 137

Acknowledgements..... 137