Smalltalk and Object Orientation: an Introduction - Free

Figure 12.3: Defining the initialize method in the Organizer class
12.5 A class side method
We shall now do something we have not yet done. We shall define a class method. To do this, first
select the class radio button below the class list window. You will n ow be on the class side of the
Organizer class. You should see that the code view window has changed and now indicates the class
instance definition. You will also see that your initialize-release protocol and initialize message
have disappeared. This is b ecause you are now on the class side and they are part of the instance side
definitions.
We are now going to define a class message protocol. Just as before, to do this you must first define
the protocol name. You do this using the right button menu in the protocol window. Call the new
protocol “instance creation ”. Now define a method in the code view window called new. Follow the
example illustrated below exactly.
new
^super new initialize
Note you must make sure th at you include the return symbol “^”, otherwise you will get the class
Organizer returned in response to the message new, rather than the new instance you wanted. The
main purpose of this method is to make sure that the instance method initialize is sent to the new
instance of an Organizer, before anything else happens. This is a common use for redefining new, i.e.
doing something before anything else can get its hands on it. The System Full Browser (available with
the advanced toolkit) is illustrated in Figure 12.4. This figure presents the state of the system after the
class side method has been defined.
Figure 12.4: Defining the class side new method
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