Smalltalk and Object Orientation: an Introduction - Free

Figure 8.1: Defining a new class
8.2.2 Defining a class comment
The next thing you should do is to define the class comment. It is generally a good idea to do this, but if
you wish to omit it, it will not effect how your class operates. If you do wish to add a comment then
select the comment option off the menu presented from the right mouse button (middle on a three
button mouse) in the class window. The comment I have defined is illustrated in Figure 8.2. Once you
have typed in the text of your comment you must “accept it”. This can be done from the right mouse
button (middle button on a three button mouse).
This is a good example of some common uses of the class comment. Note tha t I have not only
specified the intention of the class, what the instance variable of the class are and what they take, but
also how the class might be used.
8.3 Defining methods
Now you are ready to start defining methods for the class. The first method you s hould define is one
which will be used to initialize the instance’s state (i.e. initialize the instance variables). Traditionally,
methods such as initialize, which are not intended for general use, are placed in a method protocol
called “initialize-release”. If you look at the methods defined in the system classes you will note that
similar names are used for protocols possessing similar types of methods, “initialize -release” is an
example of such a protocol name. You should therefore place the method initialize within the
protocol private.
8.3.1 The “initialize-release” protocol
To create the initialize method, you will first have to create the message protocol in which to place the
method definition. To do this, you use the add option off the right button menu (middle if you have a
three button mouse) in the message protocol window. This is the third window along in the System
Browser. This causes a dialog to be displayed requesting the name of the new protocol. This will either
be blank or contain the name of the last protocol you visited. If it is not initialize-release, then type in
“initialize-release”. Again the new protocol will be either placed at the end of the list of protocols or it
will be placed above the protocol currently selected (if one is selected).
You will then be presented with a new message protocol in the message protocol window. This
protocol will be selected and the following template will be displayed in the code window:
message selector and argument names
"comment stating purpose of message"
| temporary variable names |
statements
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