Smalltalk and Object Orientation: an Introduction - Free

this convention at the moment, however it is used throughout Smalltalk , it is therefore advisable to use
it.
age: anInteger
"This method sets age."
age := anInteger
This method illustrates another feature of Smalltalk programming style, the use of class names as
parameter variable names. For example, in this method we a re expecting one parameter. Smalltalk is
untyped, therefore the contents of this parameter could be anything. However, the programmer of this
method has indicated to us that they expect the value passed into the method to be an integer. At least
now, if the system encounters a run time error and we enter the debugger, we can see if the contents of
anInteger is an integer or not. If it is not, then we may have found the source of the problem.
Figure 8.3: The System Browser displaying part of the Person definition
The equivalent methods for accessing and updating the value of the instance variable name are
presented below. They are very simple and should not come as a surprise. They are therefore mer ely
listed and are not discussed in detail.
name
"This retrieves the contents of name."
^name
name: aString
"This sets the contents of name."
name := aString
8.3.3 The “updating” protocol
Having defined all the methods for the “accessing” protocol, we will now define a new protocol called
“updating”. This protocol should be created in exactly the same way as the last two protocols. This
protocol is intended for methods which cause a change in the state of the object due to some calculation
or operation. This protocol will be used to define the birthday method (see Figure 8.4).
Figure 8.4: Defining the birthday message
This last method uses the other methods in order to change the current value of the instance variable
age and to print a meaningful message to the user.
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