Discovering Classes and Objects - Beginning Java 7 - page 168

Forbrevity,Ihaveomittedfromthe Animal hierarchy abstract Robin ,
Canary , Trout , and Salmon classes that generalize robins, canaries,
trout, and salmon. Perhaps you might want to include these classes in the
hierarchy.
Althoughthisexerciseillustratestheaccuratemodelingofanaturalscenario
usinginheritance,italsorevealsthepotentialfor class explosion —toomany
classes may be introduced to model a scenario, and it might be difficult to
maintain all these classes. Keep this in mind when modeling with inherit-
ance.
3. Continuing from the previous exercise, declare an Animals class with a
main() method.Thismethodfirstdeclaresan animals arraythatisini-
tializedto AmericanRobin , RainbowTrout , DomesticCanary ,and
SockeyeSalmon objects. The method then iterates over this array, first
outputting animals[i] (which causes toString() to be called), and
then calling each object's eat() and move() methods (demonstrating
subtype polymorphism).
4. Continuingfromthepreviousexercise,declarea public Countable in-
terfacewitha String getID() method.Modify Animal toimplement
Countable andhavethismethodreturn kind 'svalue.Modify Animals
to initialize the animals array to AmericanRobin , RainbowTrout ,
DomesticCanary , SockeyeSalmon , RainbowTrout , and Amer-
icanRobin objects.Also,introducecodethatcomputesacensusofeach
kindofanimal.Thiscodewillusethe Census classthatisdeclaredin List-
ing 2-50 .
Listing 2-50. The Census class stores census data on four kinds of animals
public class Census
{
public final static int SIZE = 4;
private String[] IDs;
private int[] counts;
public Census()
{
IDs = new String[SIZE];
counts = new int[SIZE];
}
public String get(int index)
{