Software Engineering for Students A Programming Approach

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CHAPTER 13 Refactoring This chapter: ■ explains how to carry out refactoring ■ explains several common refactorings. 13.1 ● Introduction Refactoring is about improving an architectural design. Nowadays a design tends to be an OOD, expressed in terms of classes and their interrelationships (methods). However, design does not usually proceed in a straightforward, linear manner. Most often, design tends to be an iterative process. First, candidate classes are identified. Then some will be accepted while others will be rejected – perhaps because they have no methods or because their methods are subsumed by some other class. Methods tend to migrate from one class to another as a better understanding of the objects and their role within the problem emerges. This process is known as refactoring. Refactoring is the transformation of a correct program structure (e.g., a class diagram) into an improved structure. Good ideas for refactoring are published in catalogs. Each idea has a name so that it can be referred to in conversations between developers. In this chapter we present some of the most popular refactorings. We use as an example the cyberspace invaders game (Appendix A) whose architecture is designed in the chapter on OOD. So, the steps of refactoring are: 1. create a design 2. review the design 3. identify possible refactorings 4. carry out refactoring.
166 Chapter 13 ■ Refactoring > An alternative approach is to refactor periodically as design proceeds: 1. carry out some partial design 2. review the design 3. identify possible refactorings 4. carry out refactoring 5. continue from step 1. The term coupling describes the interaction between components, while cohesion describes the interactions within a component. Many of the refactorings are aimed at minimizing coupling between components and maximizing cohesion within components. This combination promotes clarity, modularity and re-use. 13.2 ● Encapsulate Data A variable is defined as public and it is therefore unclear who uses it and why. The remedy is to make it private and provide methods to access the data. For example, in the game, the x coordinate of an alien could be declared (in Java) as: public int x; Instead, declare x as follows: private int x; And provide methods to read the value and change the value: public void setX(int newX) { x = newX; } public int getX() { return x; } Encapsulating data makes it clear how data is being accessed and by whom. Data declared as public can be accessed by any part of the software in an uncontrolled fashion. Encapsulation is one of the central features of OOP. This refactoring can always be used on any public data and its implementation is straightforward. >
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Software Engineering for Students D
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We work with leading authors to dev
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Pearson Education Limited Edinburgh
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vi Contents Part D ● Verification
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viii Detailed contents 3 The feasib
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x Detailed contents 9 Data flow des
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xii Detailed contents 14.7 Repetiti
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xiv Detailed contents 19.7 Unit tes
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xvi Detailed contents 26 Agile meth
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xviii Detailed contents 32.4 Softwa
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xx Preface Software Engineering and
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xxii Preface are engaged on a proje
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CHAPTER 1 This chapter: ■ reviews
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1.3 The cost of software production
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100% 10% 1970 SELF-TEST QUESTION Ha
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Analysis and design 1 /3 Coding 1 /
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SELF-TEST QUESTION 1.7 Maintenance
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1.8 Reliability 13 in the first pla
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1.8 Reliability 15 contain a comma
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Ease of maintenance Reliability Con
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Exercises 19 • Exercises These ex
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Further reading 21 Analyses of the
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■ documentation ■ maintenance
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2.2 The tasks 25 An important examp
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2.4 Methodology 27 reality. Like an
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■ error free ■ fault ■ tested
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3.2 ● Technical feasibility 3.3 C
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3.5 Case study 33 The hardware cost
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Answers to self-test questions 3.1
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4.2 The concept of a requirement 37
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4.3 The qualities of a specificatio
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4.5 The requirements specification
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4.6 The structure of a specificatio
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4.7 ● Use cases 4.7 Use cases 45
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Summary The ideal characteristics o
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Further reading 49 Further reading
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CHAPTER 5 This chapter explains: 5.
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5.3 Styles of human-computer interf
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5.5 Design principles and guideline
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5.5 Design principles and guideline
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SELF-TEST QUESTION 5.2 What problem
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5.8 Help systems 63 Our plan is to
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Further reading 65 5.5 Design a use
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CHAPTER 6 Modularity This chapter e
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6.2 Why modularity? 69 observed fau
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Figure 6.1 Two alternative software
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■ a simple program is more likely
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6.6 Information hiding 75 The class
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6.8 ● Coupling 6.8 Coupling 77 We
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6. Method calls with parameters tha
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3. Temporal cohesion 6.9 Cohesion 8
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> } public void setY(int newY) { y
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• Exercises 6.1 What is modularit
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CHAPTER 7 Structured programming Th
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7.2 Arguments against goto 89 If we
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■ if-then-else ■ while-do or re
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7.3 Arguments in favor of goto 93 l
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7.4 Selecting control structures 95
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while do if endif then else endWhil
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• Exercises 7.1 Review the argume
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count = 0 loop: count = count + 1 i
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> 8.2 Case study 103 A statement th
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start button event create defender
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8.3 ● Discussion Abstraction One
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Exercises 109 skill. On the other h
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CHAPTER 9 This chapter explains: 9.
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9.2 Identifying data flows 113 Noti
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Page 154 and 155: 10.5 Structure clashes 131 As seen
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Page 158 and 159: 10.6 Discussion 135 ■ teachable -
Page 160 and 161: Exercises 137 2. a control block, s
Page 162 and 163: CHAPTER 11 Object-oriented design T
Page 164 and 165: Figure 11.1 The cyberspace invaders
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Page 170 and 171: 11.7 ● Discussion Summary 147 OOD
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Page 176 and 177: 12.3 Delegation 153 The concepts of
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Page 194 and 195: Summary Summary 171 it is making po
Page 196: PART C PROGRAMMING LANGUAGES
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216 Chapter 15 ■ Object-oriented
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222 Chapter 16 ■ Programming in t
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238 Chapter 17 ■ Software robustn
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260 Chapter 18 ■ Scripting GNU/Li
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262 Chapter 18 ■ Scripting In sum
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PART D VERIFICATION
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268 Chapter 19 ■ Testing We begin
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270 Chapter 19 ■ Testing within a
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272 Chapter 19 ■ Testing Test num
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274 Chapter 19 ■ Testing if (a >=
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276 Chapter 19 ■ Testing 3. apply
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278 Chapter 19 ■ Testing made con
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280 Chapter 19 ■ Testing 19.3 Dev
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282 Chapter 19 ■ Testing 19.2 The
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284 Chapter 20 ■ Groups The term
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286 Chapter 20 ■ Groups Of course
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288 Chapter 20 ■ Groups • Exerc
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CHAPTER 21 This chapter explains: 2
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Stage Input Output 21.3 Feedback be
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Summary The essence and the strengt
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CHAPTER 22 This chapter: 22.1 ● I
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22.2 The spiral model 299 to try to
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22.4 ● Discussion Exercises 301 A
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CHAPTER 23 Prototyping This chapter
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Therefore, in summary: ■ the prod
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23.5 Evolutionary prototyping 307 U
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Reuse components 23.6 Rapid prototy
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Pitfalls For users, the problems of
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Answers to self-test questions 313
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24.2 ● Big-bang implementation 24
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Tested component Figure 24.1 Top-do
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24.7 ● Use case driven implementa
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■ middle-out ■ use case based.
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SELF-TEST QUESTION 25.1 What is the
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sharing of software or their own re
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Summary 327 Inappropriate patches,
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Further reading 329 Cathedral and t
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These are qualified by the statemen
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26.3 Extreme programming 333 develo
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SELF-TEST QUESTION 26.3 Which of th
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CHAPTER 27 This chapter explains:
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Figure 27.1 The phases of the unifi
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27.5 ● Iteration 27.6 Case study
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The transition phase Summary 343 Th
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PART F PROJECT MANAGEMENT
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348 Chapter 28 ■ Teams The commun
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350 Chapter 28 ■ Teams Level of s
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352 Chapter 28 ■ Teams A chief pr
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354 Chapter 28 ■ Teams benefits o
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356 Chapter 28 ■ Teams • Furthe
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358 Chapter 29 ■ Software metrics
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372 Chapter 30 ■ Project manageme
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31.3 Case study - assessing verific
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31.5 A single development method? 3
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Further reading 391 31.2 Draw up a
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32.3 ● The world of programming l
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32.5 ● The real world of software
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32.6 Control versus skill 397 Final
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Formal methods 32.7 Future methods
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Summary 401 In the short-term futur
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Further reading 403 An extensive tr
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APPENDIX A Case studies are used th
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Figure A.1 Cyberspace invaders A.4
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APPENDIX B Glossary Within the fiel
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C.2 ● Class diagrams C.2 Class di
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util Figure C.6 A package diagram S
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References to books and websites ar
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abstraction 99, 107 acceptance test
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fork 324 formal methods 276, 388, 3
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quality 18, 362 quality assurance 1
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Software Engineering for Students A Programming Approach

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