下列代码的运行结果是：(     )

public class Animal {
    public String noise() {return "peep"; }
    public static void main(String[] args) {
        Cat cat =null;
        Animal animal = new Dog();
        if (animal instanceof Cat) {
            cat = (Cat) animal;
            System.out.println(cat.noise());
        } else {
            System.out.println("animal is not Cat's instance"); 
        } 
    }
}
class Dog extends Animal {
    public String noise() { return "bark"; }
}
class Cat extends Animal {
    public String noise() {return "meow"; }
}