Membuat pewarisan pada java

import javax.swing.*;
class Person
{
//contruktor
private String nama;
private int usia;
public Person (String n,int u)
{
nama=n;
usia=u;
}
public String getnama()
{
return nama;
}
public int getusia()
{
return usia;
}
public void info()
{
JOptionPane.showMessageDialog(null, "Nama: "+nama);
JOptionPane.showMessageDialog(null, "Usia: "+usia);
}
}
//pewarisan
class mahasiswa extends Person
{
private int nim;
private String Strata;
public mahasiswa(String nama,int usia,int nim,String Strata)
{
super(nama,usia);
this.nim=nim;
this.Strata=Strata;
}
public void info()
{
JOptionPane.showMessageDialog(null,"nama : "+super.getnama());
JOptionPane.showMessageDialog(null, "usia : "+super.getusia());
JOptionPane.showMessageDialog(null, "nim : "+this.nim);
JOptionPane.showMessageDialog(null, "strata: "+this.Strata);
}
}
//main
class belajarpewarisan
{
public static void main(String []args)
{
Person p=new Person("ari",21);
mahasiswa m=new mahasiswa("leo",12,121,"s1");
p.info();
m.info();
}
}