Smalltalk and Object Orientation: an Introduction - Free

the name is in the address book, it will be displayed in the address book field. If not a warning message
will be displayed.
28.4 Summary
You have now created a VisualWorks GUI application. This a pplication provides you will the basics of
an address book. Of course, if you quit from the window you will lose all the names and addresses you
have input. We will look later at how you can store the dictionary used for the names and addresses into
a file so that you can access it again. The method we will use is called the Binary Object Streaming
Service (or BOSS for short). It is better than saving straight ASCII, as it perseveres the objects rather
than just plain text (where you would have to reconstruct the dictionary from the text).
An important point to consider is how we have structured this application. We have effectively
bound the address book functionality into the user interface. This is not particularly good style, however
for such a small app lication it seemed acceptable. A better structure would have been to construct a
graphical interface which used the facilities defined in the original Organizer class.
28.5 The visual Financial Manager application
This is an exercise for you the reader. This ap plication builds on the FinancialManager you have
been constructing at various times throughout this book. The aim of this exercise is to provide a
graphical interface to this application. The graphic interface should allow the user to:
1. Add deposits to the account for a specified amount.
2. Make payments (withdrawals) from the account for specified accounts.
3. Get the current balance and print a statement of all payments and deposits.
You should define the window independently of the FinancialManager class. This means that you
can make the GUIFinancialManager class a subclass of ApplicationModel. You should then
provide an instance variable in which the actual FinancialManager object will be held. This could
be done in an initialize method. I have assumed that the two input/output aspects are amount
and balance. These could also be initialized in this method. For example:
initialize
super initialize.
account := FinancialManager new.
amount := 0.00 asValue.
balance := 0.00 asValue.
In the above example, account is an instance variable used to hold the FinancialManager
object. Note that we must first send the message super initialize to ensure that the inherited
initialization is performed.
It should now be possible to write methods to handle user inputs in the form of button clicks which
pass the appropriate information onto the object held in account. For example (Note this assumes that
the amount to be input field is called “amount”):
deposit
account deposit: (amount value).
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