Smalltalk and Object Orientation: an Introduction - Free

Figure 12.2: The Organizer class definition
The class comment has been defined as follows. Remember providing a class comment is a good
habit to get into.
Class: Organizer Author: John Hunt Date: 27 September 1995
Purpose: This is a class definition which provides some of the facilities of a
personal Organizer.
History:
27 September 1995 John Hunt New Class
Instance variables:
addressBook Holds names and addresses.
Appointments Holds dates and things to do.
notes Scratch pad for notes
Usage:
To try the class out select the following and 'do it'.
|temp |
temp := Organizer new.
temp newAddress: 'Room 47' for: 'John'.
temp newAddress: 'Room 46' for: 'Patrick'.
temp newAppointment: 'Meet with MEng' for: '10/10/95'.
temp addNote: 'I must do all my work'.
temp addNote: 'Today is a brand new day'.
temp addressFor: 'John'.
temp appointmentFor: '10/10/95'.
temp printNotes.
temp inspect.
12.4 The initialize-release protocol
The first protocol we will define will be the “initialize -release” protocol. As usual we will define the
initialize method. This method will be us ed to initialize each of the instance variables with appropriate
objects. This is necessary for the other methods to function correctly. The addressBook is initialized
to hold a Dictionary object as is the appointments instance variable, while the notes instance
variable holds a Bag. Note however, that we do not access the instance variables directly, even though
we can as we are within the same class. This is because, by using the updater methods we can ensure
that any modification relating to how the Orga nizer class represents an addressBook, appointments or
notes will be localized to the methods which access and update the instance variables. Otherwise, if we
changed the internal representation we would have to modify every method which accessed them. Thi s
could make maintenance very difficult.
Figure 12.3 illustrates the System Browser with the initialize method for the Organizer class. Your
definition should look like this.
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