I have a problem with the solution

Question

import java.util.*;
public class Group extends HashSet<Person>{
    public static void main(String[] args){
    Group g = new Group();
    g.add(new Person("Hans"));
    g.add(new Person("Lotte"));
    g.add(new Person("Jane"));
    g.add(new Person("Hans"));
    g.add(new Person("Jane"));
    System.out.println("Total:" + g.size())
    public boolean add(Object o){
    System.out.println("Adding: " + o);
    return super.add(o);
    class Person{
       private final String name;
       public Person(String name){this.name = name;}
       public String toString(){return name;}
    }Which of the following occur atleast once when the code is compiled and run
Ans: The code does not compile, the problem here is in groups add method. It should have been add(Person) since the class extends HastSet<Person>. So this doesnt comple.
What would happen if you fixed this code changing add(Object) to add(Person).
My problem is if we changed add(Object) to add(Person) we will have to change the implementation in the Group class also for the following code
g.add(new Person("Hans"));
    g.add(new Person("Lotte"));
    g.add(new Person("Jane"));
    g.add(new Person("Hans"));
    g.add(new Person("Jane"));to something like
g.add("Lotte");am i correct in my inference?

Answer 1

I don't see the use of your Group class in any case. It is just a wrapper around HashSet.
Anyway, the HashSet uses generics to fix the exact dilemma that you have (being able to safely store different types of objects in it without having to subclass it for every object type), so if you want to be able to use your Group class to behave in the same way you'll have to make it using a generic type as well. Something like:
public class Group<T> extends HashSet<T>{
public boolean add(T o){
    return super.add(o);
public static void main(String[] args){
    Group<Person> g = new Group<Person>();
}(Typed from memory, could have a typo)