Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

We show the CreditCard class in Code Fragment 1.5. Note that the
CreditCard class defines five instance variables, all of which are private to the
class, and it provides a simple constructor that initializes these instance variables.
It also defines five accessor methods that provide access to the current values of
these instance variables. Of course, we could have alternatively defined the instance
variables as being public, which would have made the accessor methods moot. The
disadvantage with this direct approach, however, is that it allows users to modify an
object's instance variables directly, whereas in many cases such as this, we prefer to
restrict the modification of instance variables to special update methods. We
include two such update methods, chargeIt and makePayment in Code
Fragment 1.5.
In addition, it is often convenient to include action methods, which define specific
actions for that object's behavior. To demonstrate, we have defined such an action
method, the printCard method, as a static method, which is also included in
Code Fragment 1.5.
The Test Class
We test the CreditCard class in a Test class. Note the use of an array,
wallet, of CreditCard objects here, and how we are using iteration to
make charges and payments. We show the complete code for the Test class in
Code Fragment 1.6. For simplicity's sake, the Test class does not do any fancy
graphical output, but simply sends its output to the Java console. We show this
output in Code Fragment 1.7. Note the difference between the way we utilize the
nonstatic chargeIt and make-Payment methods and the static printCard
method.
Code Fragment 1.5: The CreditCard class.
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