JavaSE 第十九讲 多态详解 10.5

public class PolyTest
{
    public static void main(String[] args)
    {
           //Parent parent = new Parent();
           //parent.sing();
           
        //Child child = new Child();
        //child.sing();

        Parent p = new Child();
        p.sing();
    }   
}

class Parent
{
    public void sing()
    {
        System.out.println("parent is singing");
    }
}

class Child extends Parent
{
    public void sing()
    {
        System.out.println("child is singing");
    }
}

public class PolyTest2
{
    public static void main(String[] args)
    {
        //Animal animal = new Animal();
        //animal.sing();

        //Dog dog = new Dog();
        //dog.sing();

        //Animal a = new Dog();//父类的引用指向子类的对象
        //a.sing();

        Animal a = new Dog();
        Dog dog = (Dog)a;
        dog.sing();

        Animal b = new Cat();
        Dog dog = (Dog)b;
        dog.sing();//可编译，却无法执行。变量b指向Cat()对象

    }
}

class Animal
{
    public void sing()
    {
        System.out.println("animal is singing");
    }
}

class Dog extends Animal
{
    public void sing()
    {
        System.out.println("dog is singing");
    }
}

class Cat extends Animal
{
    public void sing()
    {
        System.out.println("cat is singing");
    }
}