谁能为我解释一下这个程序？？

Question

import java.util.*;
class Exam12{
public static void main(String[ ] args){
ArrayList al = new ArrayList();
al.add(new Cat("Jack"));
al.add(new Dog("Tiger"));
System.out.println((Cat)al.get(0));
System.out.println((Dog)al.get(1));
}
}
class Cat{
String name;
public Cat(String name){
this.name = name;
}
public String toString(){
return "cat: " + name;
}
}
class Dog{
String name;
public Dog(String name){
this.name = name;
}
public String toString(){
return "dog: " + name;
}
}

Answer 1

输出
cat:Jack
dog:Tiger