[7급 국가직 프로그래밍언어론 2007년 9번]

class People { 
    public void hello() {
        System.out.println("Hello !"); }
    public void introduce() {
        System.out.println("Hi !"); } 
}
class Student extends People {
    public void introduce() { hello(); } 
}
class Main {
   public static void main(String args) {
      People p = new People();
      Student s = new Student();
      call(p);
      call(s);
   }
   static void call(People p) { p.introduce(); }
}