Smalltalk and Object Orientation: an Introduction - Free

You can now define the initialize method. In this case, the method is very simple as it merely sets
the instance variable age to 0 and name to a null string ''. To do this type in the following method
definition into the code view window, replacing the method template displayed there.
initialize
"This method is used to initialize any variables etc."
self name: ''.
self age: 0.
Once you have typed in the method you can accept it. When you do so, the system will inform you that
the two methods age: and name: are undefined 8 . From the dialogs you should select the proceed
option as we will define these methods later. Figure 8.3 illustrates the System Browser at this point.
Figure 8.2: Defining a class comment
8.3.2 The “accessing” protocol
Now we will define the “accessing” protocol. Again this is a protocol name which is widely used within
the system classes. If yo u adhere to the standard protocol names you will find it easier to follow the
system classes (and other peoples classes). Define the new protocol as before and then define input the
following method.
age
"This is an example accessor method"
^age
This is an example of another feature of Smalltalk style, that is, if you write a method to return an
instance variable’s value, you do not call it returnAge, instead you give it the same name as the instance
variable; in this case age. The system is able to det ermine whether you mean the instance variable or
the method from the way you call it. These methods are termed accessor methods.
The next method will be called age: this illustrates another Smalltalk style element in this
example. This method updates an instance variable. The method is therefore given the same name as the
instance variable but with a trailing colon. We do not call it setAge: or updateAge:. You may not like
8
Note that if you have objects in the system which define these messages, then VisualWorks will not tell you that they are
undefined, even though they are undefined for Person!
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