public class Human{
    String imie;
    String nazwisko;
    int wiek;
    public Human(String nazwisko, String imie, int wiek){
        this.nazwisko=nazwisko;
        this.imie=imie;
        this.wiek=wiek;
    }
    public int hashCode(){
        return wiek;
    }
    public boolean equals(Object obj){
        Human otherHuman= (Human) obj;
        return nazwisko.equals(otherHuman.nazwisko);
    }

    public static void main(){
           Human human1 = new Human("Jan", "Kowalski", 85);
           Human human2 = new Human("Jan", "Lis", 20);
           Human human3 = new Human("Marek", "Kowalski", 20);

           System.out.println(human1 + " == " + human2 + " " + human1.equals(human2));
           System.out.println(human2 + " == " + human3 + " " + human2.equals(human3));
           System.out.println(human1 + " == " + human3 + " " + human1.equals(human3));
    }
}