Java - Polymorphism

import java.io.*;

import java.util.*;

class student

{ 

   String nam;

   int reg,ma1,ma2,ma3;



   void show(int re,String na,int m1,int m2,int m3) 

    { 

      reg = re;

      nam = na;

      ma1 = m1;

      ma2 = m2;  

      ma3 = m3;

      System.out.println("\nStudents Details");

      System.out.println("\nRegister Number : "+reg);

      System.out.println("\nName : "+nam);

      System.out.println("\nMark1 : "+ma1);

      System.out.println("\nMark2 : "+ma2);

      System.out.println("\nMark3 : "+ma3);

    } 

} 



class placedstudent extends student 

{ 

  void show(int re,String na,int m1,int m2,int m3) 

    { 

      reg = re;

      nam = na;

      ma1 = m1;

      ma2 = m2;  

      ma3 = m3;

      System.out.println("\nPlaced Students Details");

      System.out.println("\nRegister Number : "+reg);

      System.out.println("\nName : "+nam);

      System.out.println("\nMark1 : "+ma1);

      System.out.println("\nMark2 : "+ma2);

      System.out.println("\nMark3 : "+ma3);

} 

}

class PolyExam 

{ 

public static void main (String arg[]) throws IOException 

 { 

       String s1,na,s2,s3,s4;

       int re,m1,m2,m3;

       s1 = new String();

       s2 = new String();

       s3 = new String();



       DataInputStream sc = new DataInputStream(System.in);



       System.out.print("\nEnter the Register Number : ");

       s1 = sc.readLine();

       re = Integer.parseInt(s1);



       System.out.print("\nEnter the Name : ");

       na = sc.readLine();



       System.out.print("\nEnter the Mark1 : ");

       s2 = sc.readLine();

       m1 = Integer.parseInt(s2);



       System.out.print("\nEnter the Mark2 : ");

       s3 = sc.readLine();

       m2 = Integer.parseInt(s3);



       System.out.print("\nEnter the Mark3 : ");

       s3 = sc.readLine();

       m3 = Integer.parseInt(s3);



      student a1 =new student(); 

      placedstudent a2 = new placedstudent(); 



      a1.show(re,na,m1,m2,m3); 

      a2.show(re,na,m1,m2,m3);  

  } 

}