java 继承的学习（转）

转自：http://www.cnblogs.com/happyframework/p/3332243.html，非常感谢啊

public class test {

    /**
     * @param args
     */
    public static void main(String[] args) {
        printAnimal(new Animal());
        printAnimal(new Dog());
    }

    private static void printAnimal(Animal animal) {
        if(animal instanceof Dog){
            System.out.println("I am a " + (Dog) animal);
        }
        else
        {
            System.out.println("I am an " + animal);
        }
    }
}

class Animal {
    public String toString() {
        return "Animal";
    }
}

class Dog extends Animal {
    public String toString() {
        return "Dog";
    }
}