Smalltalk and Object Orientation: an Introduction - Free

• provide a more meaningful instance creation interface (for example, Line from: (3 @ 3) to: (5 @
5))
• ensure that certain information is provided which is necessary to instantiate the class (for
example Account newBalance: 24.00)
• force an initialization routine to be executed before any user of the object can send it any other
messages.
We shall consider the correct way to achieve the last of the above points. That is, we wish to force
the execution of an initialization method before returning the newly created instance. To do this we can
redefine the message new in the instance creation class side protocol of a class as follows:
new
^super new initialize
This method says, use the inherited method new to create a new instance of the class and
immediately send that new instance the instance message i nitialize (this is extremely good Smalltalk
style). In turn, the initialize method (defined on the class side) should have a format which follows this
pattern:
initialize
super initialize "to initialize inherited instance variables"
"initialize variables that I define"
24.4.5 Programming in terms of objects
It is all too easy when you are first starting with Smalltalk to write procedure oriented code within
methods. Indeed, in version 1.0 of VisualWorks there was code which had clearly been written by a C
or C++ programmer rather than a Smalltalk developer. In such situations the developer has been
thinking in too procedurally a manner. In Smalltalk what the programmer should try to do is to think in
terms of objects.
24.4.6 Example methods
Example methods are class side methods which illustrate how the instances of an object should be used.
They are particularly useful for complex classes which form part of a framework. In these classes it is
often difficult to comprehend how the various classes work together, with out seeing them work
together. The example methods can then be filed out in a production system as they are not required for
the correct functioning of the class.
24.4.7 Test methods
These have already been mentioned above and were discussed at length in the last few chapters.
However, they are an extremely useful tool for the developer and should be encouraged at every
opportunity.
24.5 Naming message protocols
An important style consideration for any VisualWorks developer is the naming of protocols (or message
categories). It is a good idea to follow the conventions laid down in the existing classes for two reasons:
1. your own classes will follow the same pattern as those which have already been encountered and
will thus be easier to follow for you and others
2. tools such as the Full Browser will allow you to see methods, defined in other classes higher up
the class hierarchy, in a given category. When you want to name a new category you can search
for similar methods, when you find them you can merely use the same category name.
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