我最近在看think in java，里面第11章介绍的东西看起来很吃力，我想问一下，class到底是什么？和String似的，也是一种类型马？这种类型有什么用?
import java.util.*;
class Pet {}
class Dog extends Pet {}
class Pug extends Dog {}
class Cat extends Pet {}
class Rodent extends Pet {}
class Gerbil extends Rodent {}
class Hamster extends Rodent {}
class Counter { int i; }
public class PetCount {
static String[] typenames = {
"Pet ", "Dog ", "Pug ", "Cat ",
"Rodent ", "Gerbil ", "Hamster ",
};
public static void main(String[] args) {
Vector pets = new Vector();
try {
Class[] petTypes = {
Class.forName( "c11.petcount.Dog "),
Class.forName( "c11.petcount.Pug "),
Class.forName( "c11.petcount.Cat "),
Class.forName( "c11.petcount.Rodent "),
Class.forName( "c11.petcount.Gerbil "),
Class.forName( "c11.petcount.Hamster "),
};
for(int i = 0; i < 15; i++)
pets.addElement(
petTypes[
(int)(Math.random()*petTypes.length)]
.newInstance());
} catch(InstantiationException e) {}
catch(IllegalAccessException e) {}
catch(ClassNotFoundException e) {}
Hashtable h = new Hashtable();
for(int i = 0; i < typenames.length; i++)
h.put(typenames[i], new Counter());
for(int i = 0; i < pets.size(); i++) {
Object o = pets.elementAt(i);
if(o instanceof Pet)
((Counter)h.get( "Pet ")).i++;
if(o instanceof Dog)
((Counter)h.get( "Dog ")).i++;
if(o instanceof Pug)