Smalltalk and Object Orientation: an Introduction - Free

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Object ApplicationModel Statement FinancialManager aFinancialManager account aStatement Figure 27.7: Using an ApplicationModel with an domain object The objects involved in providing the applications functionality (or domain model) no longer need to be involved in the model hierarchy, they can inherit from any class in the system. For example, if we were to link our class Statement into this architecture we would do so as indicated in Figure 27.7. In this figure the classes are indicated by rectangles and instances by round cornered boxes. The approach of separating o ut ApplicationModel functionality is extremely powerful as we can now develop the user interface and the system functionality completely separately. The following table summarizes this separation. application model domain model Provides user interface processing capabilities Provides system functionality The ApplicationModel class is actually the root of its own application model hierarchy. Figure 27.8 illustrates part of this hierarchy. As can be seen from this diag ram many of the graphical tools provided within VisualWorks are subclasses of ApplicationModel. For example, the user interface builder is provided by class such as UIBuilder, UIBuilderWatcher and UIPalette. The browsers are subclass of ApplicationModel as is the inspector, the changes tool and the file browser. The graphical class browser used to display the class hierarchies is also a (user) defined subclass of ApplicationModel. Figure 27.8: Part of the ApplicationModel hierarchy 27.6 Defining a window’s functionality We return now to the process of creating a window. So far we have defined the structure of the window but not yet how information is made available to the window (or obtained f orm the window), nor what happens when buttons are pressed etc. We have however defined the aspects for input fields (their 228
names) and the actions for buttons (the messages to send if they are selected). We can now get the system to define these for us aut omatically. This is done using the ‘Define’ option from the canvas tool. This brings up the definer window as illustrated in Figure 27.9. This allows the user to select which aspects and which actions they wish to define. This can be used to ensure that modifications made to the definitions by the developer do not get over written. Figure 27.9: The Definer Different things happen to inpu t fields (and to lists and tables) than to action buttons. In the case of an input field the system defines an instance variable on the class and creates an accessor method as illustrated in Figure 27.10. This accessor method also provides a lazy initialization approach to the instance variable. For an action the definer merely creates a stub method which returns self. This ensure that when the window is created an exception is not generated when a button is pressed. Th e user is then able to redefine the action methods to perform the desired operations. Figure 27.10: The defined entry aspect 27.7 Initialization It is important when using an a pplication model to ensure that any initialization performed does not overwrite that accomplished higher up in the ApplicationModel class hierarchy. For example, in Figure 27.11 we define an initialization method for th e simple to do list Organizer presented in Figure 27.12. The first thing that this method does is to send a message initialize up the class hierarchy using: super initialize. This ensures that the initialization steps performed by the ApplicationModel will be carried out first. This is essential because if initialize merely overwrote the inherited method, then the user 229
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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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een to ease the transition from one
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encapsulation. Attempting to introd
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is a controversial subject which is
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will become second nature to many o
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or return something. It has since b
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defining the behavior of different
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In time most developers start to ac
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2.4.3.4 Smalltalk environments are
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3. Constructing an Object Oriented
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Wash wipe switch Wiper motor Relay
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Point 2 above is more complicated.
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services working? working? working?
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Part Two The Smalltalk Language 42
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other systems. As the browsers, ins
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VisualAge (a version of Smalltalk w
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4.5.2 The VisualWorks Launcher and
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Class categories. These are group s
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5. A Little Smalltalk 5.1 Introduct
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Notifiers can be displayed under a
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These concepts of messages, receive
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Select the “Debug” option. This
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6. Smalltalk Building Blocks 6.1 In
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6.3.1 Class definitions In Smalltal
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Object Class1 Class 2 method search
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“Now calculate y “ y := x * 23.
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7. Smalltalk Constructs 7.1 Introdu
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They are more efficient for storage
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7.5.3 true, false and nil variables
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anArray at: 1 max: 10. This will tr
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Figure 8.1: Defining a new class 8.
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this convention at the moment, howe
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9. Control and Iteration 9.1 Introd
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9.3.3 Block temporary variables Blo
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The brackets round the 1 to: 10 are
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OrderedCollection class (respective
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holding other objects. Typically, c
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| temp | temp := Set new. temp add:
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Next we will define a message proto
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11. Further Collection Classes 11.1
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for (i = 0; i
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x inspect. This has some similariti
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11.9.3 The reject: message The reje
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• asSortedCollection. This create
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Figure 12.2: The Organizer class de
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12.6 The private-updating protocol
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do: [:item | Transcript show: item
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13. Streams and Files 13.1 Introduc
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Notice that in this example we used
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to reconstruct the data into object
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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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Page 179 and 180: 21.5.5 Running the editor You have
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Page 183 and 184: made worse, because the symbol held
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Page 189 and 190: 22.7.2 The Perform: message The per
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Page 203 and 204: Table 24.2: Class message categorie
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Page 217 and 218: Figure 26.5: Part of the Controller
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Page 247 and 248: DrawingView model SmallDraw drawing
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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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