testpoly.java

java课件

class TestPoly {
  public static void main(String[] args) {
    m(new GraduateStudent());
    m(new Student());
    m(new Person());
    m(new Object());
  }
  public static void m(Object x){
    System.out.println(x.toString());
  }
}       
class GraduateStudent extends Student{
}
class Student extends Person{
  public String toString(){
    return "Student";
  }
}
class Person extends Object{
  public String toString(){
    return "Person";
  }
}