Software Engineering for Students A Programming Approach

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CHAPTER 11 Object-oriented design This chapter: ■ explains how to carry out object-oriented design (OOD) ■ explains how to use class–responsibility–collaborator (CRC) cards ■ emphasizes the importance of using ready-made libraries. 11.1 ● Introduction We begin this chapter by reviewing the distinctive features and principles of objectoriented programming (OOP). This sets the scene as to what an OOD seeks to exploit. Then we look at how to go about designing software. We use the Cyberspace Invaders game as the case study. The widely agreed principles of OOP are: ■ encapsulation ■ inheritance ■ polymorphism. The advantages of these features is that they promote the reusability of software components. Encapsulation allows a class to be reused without knowing how it works – thus modularity and abstraction are provided. Inheritance allows a class to be reused by using some of the existing facilities, while adding new facilities in a secure manner. Polymorphism further promotes encapsulation by allowing general purpose classes to be written that will work successfully with many different types of object. Object-oriented languages are usually accompanied by a large and comprehensive library of classes. Members of such a library can either be used directly or reused by employing inheritance. Thus the process of programming involves using existing library classes, extending the library classes, and designing brand-new classes. During OOD, the designer must be aware of the wealth of useful classes available in the libraries. To ignore them would be to risk wasting massive design, programming
140 Chapter 11 ■ Object-oriented design and testing time. It is common experience for someone setting out to write OO software to find that nearly all of the software already exists within the library. OO development is therefore often regarded as (merely) extending library classes. This, of course, requires a discipline – the initial investment in the time to explore and learn about what might be a large library, set against the benefits that accrue later. 11.2 ● Design One of the principles used in the design of object-oriented software is to simulate real world situations as objects. You build a software model of things in the real world. Here are some examples: ■ if we are developing an office information system, we set out to simulate users, mail, shared documents and files ■ in a factory automation system, we set out to simulate the different machines, queues of work, orders, and deliveries. The approach is to identify the objects in the problem to be addressed and to model them as objects in the software. One way to carry out OOD is to examine the software specification in order to extract information about the objects and methods. The approach to identifying objects and methods is: 1. look for nouns (things) in the specification – these are the objects 2. look for verbs (doing words) in the specification – these are the methods Here is the specification for the cyberspace invaders program: A panel (Figure 11.1) displays a defender and an alien. The alien moves sideways. When it hits a wall, it reverses its direction. The alien randomly launches a bomb that moves vertically downwards. If a bomb hits the defender, the user loses and the game is over. The defender moves left or right according to mouse movements. When the mouse is clicked, the defender launches a laser that moves upwards. If a laser hits the alien, the user wins and the game is over. A button is provided to start a new game. Scanning through the specification, we find the following nouns. As we might expect, some of these nouns are mentioned more than once, but the repetition does not matter for the purpose of design. panel, defender, alien, wall, bomb, mouse, laser These nouns correspond to potential objects, and therefore classes within the program. So we translate these nouns into the names of classes in the model. The noun panel translates into the Panel class, available in the library. The nouns defender and alien translate into the classes Defender and Alien respectively. The noun wall
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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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Page 116 and 117: 7.3 Arguments in favor of goto 93 l
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Page 122 and 123: • Exercises 7.1 Review the argume
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Page 126 and 127: > 8.2 Case study 103 A statement th
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Page 130 and 131: 8.3 ● Discussion Abstraction One
Page 132 and 133: Exercises 109 skill. On the other h
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Page 136 and 137: 9.2 Identifying data flows 113 Noti
Page 138 and 139: 9.3 Creation of a structure chart 1
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Page 142 and 143: Exercises 119 During the second sta
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Page 146 and 147: In English, this reads: 10.2 A simp
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Page 152 and 153: Process header Process issue 10.4 M
Page 154 and 155: 10.5 Structure clashes 131 As seen
Page 156 and 157: 10.5 Structure clashes 133 Let us r
Page 158 and 159: 10.6 Discussion 135 ■ teachable -
Page 160 and 161: Exercises 137 2. a control block, s
Page 164 and 165: Figure 11.1 The cyberspace invaders
Page 166 and 167: SELF-TEST QUESTION 11.1 Derive info
Page 168 and 169: 11.5 Class-responsibility-collabora
Page 170 and 171: 11.7 ● Discussion Summary 147 OOD
Page 172 and 173: 11.11 Compare and contrast the prin
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Page 176 and 177: 12.3 Delegation 153 The concepts of
Page 178 and 179: 12.5 Factory method 155 The followi
Page 180 and 181: 12.8 Model, view controller (observ
Page 182 and 183: Figure 12.4 Pipe and Filter pattern
Page 184 and 185: Figure 12.6 Layers in a distributed
Page 186 and 187: Answers to self-test questions 163
Page 188 and 189: CHAPTER 13 Refactoring This chapter
Page 190 and 191: 13.3 ● Move Method 13.6 Inline Cl
Page 192 and 193: class Sprite Instance variables x y
Page 194 and 195: Summary Summary 171 it is making po
Page 196: PART C PROGRAMMING LANGUAGES
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190 Chapter 14 ■ The basics Ada d
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192 Chapter 14 ■ The basics The w
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194 Chapter 14 ■ The basics In a
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196 Chapter 14 ■ The basics > str
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198 Chapter 14 ■ The basics Answe
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CHAPTER 15 Object-oriented programm
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202 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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