public class PolymorphismDemo $\{$

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";

$\}$

$\}$

could you please Modify then Explain the code?

Here is exaple of

could you please write it in this way?

import java.util.ArrayList;

import java.util.Scanner;

public class Main $\{$

public static void main$($String$[]$ args$)\{$

ArrayList