Smalltalk and Object Orientation: an Introduction - Free

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anObject MyCar totalNumber A capitalization convention is used consistently throughout Smalltalk and most Smalltalk programmers adhere to this standard which it is therefore advisable to follow: • Private variables (instance/temporary variables) start with a lower-case letter. • Shared variables (class/global/ pool variables) start with an upper-case letter. Note that message selectors should start with a lower-case letter. Another convention worth noting is that if a variable or a message selector combines two or more words, the convention is to capitalize the first letter of the second word onwards. E.g. displayTotalPay, returnStudentName. If we consider our new method above, we have still to consider what happens in the assignment statement (:=). We shall look at this in the next chapter along with the range of arithmetic functions available. 68
7. Smalltalk Constructs 7.1 Introduction This chapter presents more of the Smalltalk language. Section two considers the representation and use of numbers in Smalltalk while Section three considers strings and characters. Section four discu sses variables in Smalltalk and Section five literals and variables. Sections six considers messages, message types and their precedence. 7.2 Numbers and operators 7.2.1 Numeric values in Smalltalk Numbers in Smalltalk are all objects, that means that they are ins tances of a class. For example, integer numbers such as 2 are an instance of the class SmallInteger. In fact there are a number of classes which together provide for the types of numbers normally used, these include SmallInteger, LargePositiveInteger, LargeNegativeInteger, Float and Double. These will all be considered in greater detail later in the book. For the moment we will just consider what numbers look like in Smalltalk. Just as in most programming languages, a numeric value in Smalltal k is a series of numbers which may or may not have a preceding ‘-’ and may contain a decimal point. For example: 25 -10 1996 12.45 0.13451345 -3.14 It is also possible to specify numbers in bases other than 10. This is done by preceding the number with the base and the letter r (which stands for radix). For example: 2r101 16r452 Numbers can also be expressed using scientific notation using the ‘e’ (for exponent) or ‘d’ (for double-precision) suffix plus the exponent in decimal. For example: 10e3 which equals 1000 In addition to integers and real numbers, Smalltalk also explicitly supports fractions (e.g. 7/8) and radians. In all other ways numbers in Smalltalk are just like numbers in any other language. 7.2.2 Arithmetic operators Table 7.1: Numeric operators + addition * multiplication - subtraction / division / / modulus quo quotiant rem remainder \ \ remainder from modulo division < less than greater than >= greater than or equal to max: maximum min: minimum ceiling roundup floor round down 69
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Smalltalk and Object Orientation: A
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Chapter 7: Smalltalk Constructs Thi
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The user interface construction fac
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Preface 1. INTRODUCTION TO OBJECT O
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12.5 A CLASS SIDE METHOD...........
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27.3 VISUALWORKS WINDOW PAINTING TO
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Part One Introduction to Object Ori
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interfaces between different parts
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Page 20 and 21: encapsulation. Attempting to introd
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Page 24 and 25: will become second nature to many o
Page 26 and 27: or return something. It has since b
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Page 30 and 31: In time most developers start to ac
Page 32 and 33: 2.4.3.4 Smalltalk environments are
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Page 36 and 37: Wash wipe switch Wiper motor Relay
Page 38 and 39: Point 2 above is more complicated.
Page 40 and 41: services working? working? working?
Page 42: Part Two The Smalltalk Language 42
Page 45 and 46: other systems. As the browsers, ins
Page 47 and 48: VisualAge (a version of Smalltalk w
Page 49 and 50: 4.5.2 The VisualWorks Launcher and
Page 51 and 52: Class categories. These are group s
Page 53 and 54: 5. A Little Smalltalk 5.1 Introduct
Page 55 and 56: Notifiers can be displayed under a
Page 57 and 58: These concepts of messages, receive
Page 59 and 60: Select the “Debug” option. This
Page 61 and 62: 6. Smalltalk Building Blocks 6.1 In
Page 63 and 64: 6.3.1 Class definitions In Smalltal
Page 65 and 66: Object Class1 Class 2 method search
Page 67: “Now calculate y “ y := x * 23.
Page 71 and 72: They are more efficient for storage
Page 73 and 74: 7.5.3 true, false and nil variables
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Page 77 and 78: Figure 8.1: Defining a new class 8.
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Page 81 and 82: 9. Control and Iteration 9.1 Introd
Page 83 and 84: 9.3.3 Block temporary variables Blo
Page 85 and 86: The brackets round the 1 to: 10 are
Page 87 and 88: OrderedCollection class (respective
Page 89 and 90: holding other objects. Typically, c
Page 91 and 92: | temp | temp := Set new. temp add:
Page 93 and 94: Next we will define a message proto
Page 95 and 96: 11. Further Collection Classes 11.1
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Page 103 and 104: • asSortedCollection. This create
Page 105 and 106: Figure 12.2: The Organizer class de
Page 107 and 108: 12.6 The private-updating protocol
Page 109 and 110: do: [:item | Transcript show: item
Page 111 and 112: 13. Streams and Files 13.1 Introduc
Page 113 and 114: Notice that in this example we used
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Page 117 and 118: 1. The ability to save the current
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14.3 The class Date Class Date, a s
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aCharacter isAlphabetic. aCharacter
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Breakpoints may be placed in a me t
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If the file does not exist you will
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Figure 15.4: Creating a project To
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Part Three Object Oriented Design 1
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16. Object Oriented Analysis and De
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devolved amongst the objects). This
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driving force behind the whole of t
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17. The Unified Modeling Language 1
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Deployment diagrams . Deployment di
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Window abstract +size : Area = (10,
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Micro Computer 1.. * Monitor System
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connectedTo * Lamp * Weight Sensor
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18. UML: Dynamic Modeling And Deplo
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edisplay() Controller window A Wind
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18.2.3.1 A start point A start poin
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etween nodes and their stereotype.
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OMT is a prescriptive method, it pr
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confirming the users’ needs, thei
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19.3.2.2 Prepare a data dictionary
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car, truck and bus under a supercla
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20.2.1.3 Prepare sequence and colla
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20.2.2.5 Specify optimization crite
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are therefore concurrent and can be
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20.3.2.3 Design optimization The an
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21. Frameworks and Patterns for Obj
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As the framework takes shape you sh
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about a set of classes, than to att
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instanceVariableNames: '' classVari
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21.5.5 Running the editor You have
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Part Four Testing and Style 181
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made worse, because the symbol held
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22.3.2 Incremental testing Incremen
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control the execution of the method
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22.7.2 The Perform: message The per
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From the scenario that a person mig
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23.4 Self testing An approach, sugg
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24. Smalltalk Style Guidelines 24.1
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24.2.4 Adding variables to system c
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should use a dictionary to hold the
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• A method should only send messa
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Table 24.2: Class message categorie
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25. The Perform and Dependency Mech
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• Inheritance (class to class rel
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You can find the methods which impl
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These messages are sent automatical
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26. The Model-View-Controller Archi
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and wit hdrawals and requests for t
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Figure 26.5: Part of the Controller
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model 4. update 1. balance (view) 0
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displayed. The second component add
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27. Graphical User Interface Constr
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27.3.1 Palette The Palette tool pro
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uild a running user interface from
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names) and the actions for buttons
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Edit button, then the user interfac
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27.11 Visual reuse The aim of visua
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Figure 27.17: Defining the parent c
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important, as these facilities hand
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28.3 The AddressBook class 28.3.1 T
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The aspect methods can then be simp
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the name is in the address book, it
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29.2 The custom view widget 29.2.1
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DrawingView model SmallDraw drawing
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The action of adding a new graphic
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The next method we shall consider i
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In the updating protocol we need to
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The displaying protocol contains th
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30. Memory Management and Garbage C
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30.3.3 PermSpace This is used to ho
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31. Concurrency in Smalltalk 31.1 I
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The Semaphore class provides facili
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Once the process wakes up it can de
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31.4.3 Acknowledgments Acknowledgme
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“There are two kinds of objects i
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Object Object class Collection Coll
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ehavior, but from the point of view
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32.5.5 The whole enchilada Behaviou
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33. The Future for Object Technolog
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solutions are needed which suit the
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scripting and query language to use
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34. Appendix: The Smalltalk Languag
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A capitalization convention is used
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• marries: is the message selecto
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Array OrderedCollection SortedColle
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[Coleman et al 1994] D. Coleman, P.
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OOPSLA/ECOOP’90, Joint Conference
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detect.............................
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True...............................
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