Arrays - Java Software Solutions: Foundations of Program Design - page 400

The collection array is instantiated in the DVDCollection constructor. Every
time a DVD is added to the collection (using the addDVD method), a new DVD
object is created and a reference to it is stored in the collection array.
Each time a DVD is added to the collection, we check to see whether we have
reached the current capacity of the collection array. If we didn't perform this
check, an exception would eventually be thrown when we try to store a new DVD
object at an invalid index. If the current capacity has been reached, the private
increaseSize method is invoked, which first creates an array that is twice as
big as the current collection array. Each DVD in the existing collection is then
copied into the new array. Finally, the collection reference is set to the larger
array. Using this technique, we theoretically never run out of room in our DVD
collection. The user of the DVDCollection object (the main method in this case)
never has to worry about running out of space, because it's all handled internally.
Figure 8.3 shows a UML class diagram of the Movies program. Recall that the
open diamond indicates aggregation. The cardinality of the relationship is also
noted: a DVDCollection object contains zero or more DVD objects.
The toString method of the DVDCollection class returns an entire report sum-
marizing the collection. The report is created, in part, using calls to the toString
method of each DVD object stored in the collection. Listing 8.9 shows the DVD class.

DVDCollection

Movies

- collection : DVD[]
- count : int
- totalCost : double

+ main (args : String[]) : void

+ addDVD(title : String, director : String,
year : int, cost : double, blueray :
boolean) : void
+ toString() : String
- increaseSize() : void

1

*

DVD

- title : String
- director : String
- year : int
- cost : double
- blueray : boolean

+ toString() : String

FIGURE 8.3 A UML class diagram of the Movies program