Java面向对象：多态是编译时行为还是运行时行为

多态是编译时行为还是运行时行为？
答：运行时行为。可利用random随机数随机生成对象，在运行时产生对象，来证明多态试运行时行为。
代码：

import java.util.Random;

class Animal {
    String name = "animal";

    public String getinfo() {
        return null;
    }

}

class Cat extends Animal {
    String name = "cat";
    int age = 3;

    public String getinfo() {
        return String.format("name: %s age: %d", name, age);
    }

}

class Dog extends Animal {
    String name = "dog";
    int age = 5;

    public String getinfo() {
        return String.format("name: %s age: %d", name, age);
    }

}
public class PolymorphicDemo {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        PolymorphicDemo pd = new PolymorphicDemo();
        Animal a = pd.getInstance(new Random().nextInt(3));
        System.out.println(a.getinfo());

    }

    public Animal getInstance(int key) {
        switch (key) {
        case 0:
            return new Cat();
        case 1:
            return new Dog();
        default:
            return new Animal();

        }
    }
}

输出：

name: cat age: 3