Java多态:upcast和downcast

public class Test
{
public static void main(String[] args)
{
Cup aCup = new BrokenCup();
aCup.addWater(10); // method binding
}
}

class Cup
{
public void addWater(int w)
{
this.water = this.water + w;
}

public void drinkWater(int w)
{
this.water = this.water - w;
}

private int water = 0;
}

class BrokenCup extends Cup
{
public void addWater(int w)
{
System.out.println("shit, broken cup");
}

public void drinkWater(int w)
{
System.out.println("om...num..., no water inside");
}
}

public class TestJavaDemo{
public static void main(String[] args) {
Person p=new Student();
Student s=(Student)p;
s.fun1();
s.fun2();
}
}

class Person{
public void fun1(){
System.out.println("1.Person{fun1()}");
}

public void fun2(){
System.out.println("2.Person{fun2()}");
}
}

class Student extends Person{
public void fun1(){
System.out.println("3.Student{fun1()}");
}
public void fun3(){
System.out.println("4.Student{fun3()}");
}
}