public class Cwiczenie31 {

    public static void main(String[] args) {
        try {
            zapiszOsoby();
            odczytajOsoby();
        } catch (IOException ex) {
            ex.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
    }

    public static void zapiszOsoby() throws IOException {
        ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("osoby.data"));

        Set<Osoba> osoby = new HashSet<>();
        osoby.add(new Osoba(15, "Jan", 82.5f));
        osoby.add(new Osoba(25, "Monika", 65));
        osoby.add(new Osoba(31, "Krzysztof", 72));

        out.writeObject(osoby);
    }

    public static void odczytajOsoby() throws IOException, ClassNotFoundException {
        ObjectInputStream in = new ObjectInputStream(new FileInputStream("osoby.data"));

        Set<Osoba> osoby = (Set<Osoba>) in.readObject();

        for (Osoba osoba : osoby) {
            System.out.println(osoba.getImie());
        }
    }
}