Object-oriented Software in Ada 95

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226 Polymorphism 15.8 Self-assessment • What is an access type? What is an access value? • How is dynamic storage allocated? • What mechanisms are available to return dynamically allocated storage? • Why is dynamic storage allocation often considered a potential problem area in a program? • How do you pass a procedure as a parameter to another procedure? • Why is it essential to be able to call the procedure Finalize in the class Account more than once on the same object? • What is the difference between 'Access and 'Unchecked_Access? 15.9 Exercises Construct the following: • Store A store for data items which has as its generic parameters the type of the item stored and the type of the index used. The generic specification of the class is: generic type Store_index is private; -- type Store_element is private; -- package Class_store is type Store is limited private; -- NO copying Not_there, Full : exception; procedure add ( the:in out Store; index:in Store_index; item:in Store_element); function deliver( the:in Store; index:in Store_index ) return Store_element; private -- end Class_store; The implementation of the store uses a linked structure. • Queue The class Queue implements a data structure in which items are added to the rear of the queue and extracted from the front. Implement this generic class using dynamic storage allocation. © M A Smith - May not be reproduced without permission
16 Polymorphism In the processes described so far, when a message is sent to an object, the method executed has been determinable at compile-time. This is referred to as static binding. If the type of an object that a message is sent to is not known until run-time, the binding between the method and the message is dynamic. Dynamic binding leads to polymorphism, which is when a message sent to an object causes the execution of a method that is dependent on the type of the object. 16.1 Rooms in a building A partial classification of the different types of accommodation found in an office building is shown in Figure 16.1. Room Store Room Office Executive Office Figure 16.1 Partial classification of types of accommodation in a building. The type of accommodation in each part of the building can be modelled using the Ada inheritance mechanism. First, a class Room to describe a general room is created. This class is then used as the base class for a series of derived classes that represent more specialized types of room. For example, an executive office is a more luxurious office, perhaps with wall-to-wall carpets and an outside view. Each class derived from the class Room, including Room, has a function describe which returns a description of the accommodation. A program is able to send the message describe to an instance of any type of accommodation and have the appropriate code executed. This is accomplished with function name overloading. Figure 16.2 illustrates the call of a function describe on an instance of a class derived from Room. Room Describe Store Room Office Executive ve Office Office Figure 16.2 Call of describe on any instance of an object derived from Room. © M A Smith - May not be reproduced without permission
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Reproduction prohibited without per
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Contents CONTENTS .................
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vi Contents 4.21 EXERCISES.........
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viii Contents 10.1 INTRODUCTION ...
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x Contents 16.8.1 Converting a base
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xii Contents 23.6.3 The specificati
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Preface This book is aimed at stude
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xvi Actual parameter Preface The ph
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xviii Elaboration Preface At run-ti
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xx Object Preface An instance of a
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1 Introduction to programming 1 Int
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Introduction to programming 3 they
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Introduction to programming 5 • T
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Introduction to programming 7 The s
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Introduction to programming 9 Line
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Introduction to programming 11 Cost
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Introduction to programming 13 In t
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Introduction to programming 15 For
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Introduction to programming 17 •
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Software design 19 In software the
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Software design 21 2.4 The class In
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Software design 23 Inheritance diag
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25 Ada introduction: Part 1 3 Ada i
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Ada introduction: Part 1 27 3.3.2 C
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Ada introduction: Part 1 29 can be
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Ada introduction: Part 1 31 with Ad
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Ada introduction: Part 1 33 To inpu
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Ada introduction: Part 1 35 Functio
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Ada introduction: Part 1 37 3.14 Ex
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Note: In reality the floating point
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Ada introduction: Part 2 41 4.4 Mod
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Ada introduction: Part 2 43 4.7.2 I
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Ada introduction: Part 2 45 For exa
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Ada introduction: Part 2 47 When pe
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Ada introduction: Part 2 49 4.12 Co
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Ada introduction: Part 2 51 4.13.1
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Ada introduction: Part 2 53 Note 3
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Ada introduction: Part 2 55 if Ch i
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Ada introduction: Part 2 57 For exa
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Ada introduction: Part 2 59 type Mi
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Procedures and functions 61 The fun
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Procedures and functions 63 The maj
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Procedures and functions 65 Mode Al
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Procedures and functions 67 The pro
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Procedures and functions 69 5.8 Dif
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Procedures and functions 71 Note: T
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6 Packages as classes This chapter
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Packages as classes 75 6.3.1 An obj
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Packages as classes 77 package Clas
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Packages as classes 79 The body of
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Packages as classes 81 Thus without
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Packages as classes 83 6.9 Type pri
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Packages as classes 85 which when r
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Packages as classes 87 The Ada spec
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The main body of the program proces
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Packages as classes 91 The procedur
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Packages as classes 93 Construct th
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Data structures 95 This initializat
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Data structures 97 Then an assignme
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Data structures 99 In Ada a variant
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Data structures 101 7.10 Exercises
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which when combined with appropriat
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Arrays 105 with Ada.Text_Io, Class_
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Arrays 107 8.3.1 Putting it all tog
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Arrays 109 8.4.1 The class Board Th
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Arrays 111 8.4.4 The class Board Th
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Arrays 113 8.4.5 Putting it all tog
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Arrays 115 8.5.2 Attributes of mult
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Arrays 117 The following code would
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Arrays 119 This type is defined in
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Arrays 121 In the implementation of
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Arrays 123 The Ada specification of
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Arrays 125 The function valid check
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9 Case study: Design of a game This
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Case study: Design of a game 129 A
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Case study: Design of a game 131 Co
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Case study: Design of a game 133 Cu
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Case study: Design of a game 135 --
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The specification for the class Cel
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Case study: Design of a game 139 pr
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Case study: Design of a game 141 Th
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Case study: Design of a game 143 Th
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Case study: Design of a game 145 In
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10 Inheritance This chapter introdu
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Two instances of the class Interest
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Inheritance 151 The two classes Acc
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Inheritance 153 which when run, wou
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Inheritance 155 The specialization
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Inheritance 157 Note: The methods o
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Inheritance 159 10.7.1 Putting it a
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Inheritance 161 10.8.1 Implementati
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10.9 Hiding the base class methods
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Inheritance 165 • For an object o
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Exceptions 167 11.1.1 Putting it al
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Exceptions 169 11.3 Private child A
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12 Defining new operators This chap
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Exceptions 173 Using the above pack
Page 197 and 198: Exceptions 175 The function Rat_Con
Page 199 and 200: Exceptions 177 12.3.1 Overloading =
Page 201 and 202: Exceptions 179 The overloaded defin
Page 203 and 204: Exceptions 181 12.3.5 use type A mo
Page 205 and 206: 13 Exceptions This chapter looks at
Page 207 and 208: Exceptions 185 Note: The object Eve
Page 209 and 210: Exceptions 187 A program to demonst
Page 211 and 212: Exceptions 189 package body Class_S
Page 213 and 214: 14 Generics This chapter looks at g
Page 215 and 216: Exceptions 193 The above generic pr
Page 217 and 218: Exceptions 195 14.3 Generic stack T
Page 219 and 220: Exceptions 197 14.3.1 Putting it al
Page 221 and 222: Thus, an instantiation of a procedu
Page 223 and 224: Exceptions 201 14.5 Sorting Some of
Page 225 and 226: 14.6.1 Putting it all together Exce
Page 227 and 228: Exceptions 205 An efficient impleme
Page 229 and 230: Exceptions 207 The implementation o
Page 231 and 232: 15 Dynamic memory allocation This c
Page 233 and 234: Dynamic memory allocation 211 In a
Page 235 and 236: Dynamic memory allocation 213 One w
Page 237 and 238: Dynamic memory allocation 215 15.2.
Page 239 and 240: Dynamic memory allocation 217 The p
Page 243 and 244: Dynamic memory allocation 221 A ben
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Page 251 and 252: Polymorphism 229 This can be implem
Page 253 and 254: Polymorphism 231 16.2.1 Putting it
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Page 259 and 260: Polymorphism 237 An example interac
Page 261 and 262: Polymorphism 239 The conversion fro
Page 263 and 264: Polymorphism 241 Screen Observed Ob
Page 265 and 266: Polymorphism 243 The method Add_Obs
Page 267 and 268: Polymorphism 245 The functions vali
Page 269 and 270: Polymorphism 247 The driver program
Page 271 and 272: 17 Containers This chapter describe
Page 273 and 274: Containers 251 This mirrors closely
Page 275 and 276: Containers 253 will produce the fol
Page 277 and 278: Containers 255 When an instance of
Page 279 and 280: Containers 257 When the iterator Co
Page 281 and 282: Containers 259 In the implementatio
Page 283 and 284: Containers 261 A deep copy of this
Page 285 and 286: Containers 263 • If the objects o
Page 287 and 288: Containers 265 17.6.1 Ada specifica
Page 289 and 290: Containers 267 The procedure Adjust
Page 291 and 292: 17.7 A set Containers 269 Using as
Page 293 and 294: Containers 271 17.7.1 Putting it al
Page 295 and 296: 18 Input and output This chapter de
Page 297 and 298: Input and output 275 18.2 Reading a
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Input and output 277 Then the follo
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Input and output 279 18.5 Self-asse
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Persistence 281 A program to implem
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Persistence 283 with Ada.Strings.Un
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Persistence 285 The process to add
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Persistence 287 The procedure Add u
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20 Tasks This chapter describes the
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Tasks 291 The execution of the abov
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Tasks 293 Likewise, the task Task_I
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Tasks 295 20.4 Protected type In es
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Tasks 297 The implementation of the
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Tasks 299 to the entry prevents the
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Note: 20.7.1 Accept alternative Tas
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Tasks 303 the implementation of whi
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Tasks 305 • How can a task select
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System programming 307 21.1.1 Putti
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System programming 309 The followin
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22 A text user interface This chapt
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A Text user interface 313 Note: The
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A Text user interface 315 with Clas
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A Text user interface 317 Window_St
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A Text user interface 319 The follo
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A Text user interface 321 package C
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A Text user interface 323 with Clas
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A Text user interface 325 function
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A Text user interface 327 • What
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TUI the implementation 329 23.1.1 S
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TUI the implementation 331 package
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TUI the implementation 333 23.2.4 T
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TUI the implementation 335 with Ada
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TUI the implementation 337 The Inpu
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TUI the implementation 339 procedur
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TUI the implementation 341 New_Line
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TUI the implementation 343 private
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TUI the implementation 345 The proc
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TUI the implementation 349 with Pac
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TUI the implementation 351 Method S
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TUI the implementation 355 The proc
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24 Scope of declared objects This c
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Proc_2_2 Proc_1_1 Proc_2_1 Proc_2_2
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25 Mixed language programming This
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Mixed language programming 363 3 Tr
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Mixed language programming 365 /* *
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Appendix A 367 if Temp < 15 then Pu
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Appendix A 369 package body Class_I
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Appendix B: Components of Ada B.1 R
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T'Digits The decimal precision. Uni
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Appendix B 375 access enumeration E
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Appendix B 377 B.8.2Ada information
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Appendix C 379 package Standard is
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Appendix C 381 type Character is (n
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Appendix C 383 package Ada.IO_Excep
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Appendix C 385 --Specification of l
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Appendix C 387 procedure Get(File :
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Appendix C 389 procedure Get(Item :
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Appendix C 391 package Ada.Characte
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Appendix C 393 --Conversion, Concat
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Appendix C 395 return Natural; Goin
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Appendix C 397 Right : in Bounded_S
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Appendix C 399 Count : out size_t;
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Appendix C 401 C.14 The Package Ada
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Appendix C 403 --Storage-related De
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Appendix D 405 with Ada.Text_Io; us
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Appendix D 407 with Ada.Text_Io, Ad
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Appendix D 409 package Class_Perfor
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Appendix D 411 declare Kb : constan
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Appendix D 413 package body Class_B
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Appendix D 415 The instantiation of
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Appendix D 417 with Ada.Text_Io, Ad
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References Intermetrics (1995) Ada
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Index 421 'class, 233 Class attribu
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Index 423 + dyadic, 53 monadic, 54
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Object-oriented Software in Ada 95

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