Set set = new HashSet();
        set.add(new Person("Joe", 33, 400));
        set.add(new Person("Kris", 25, 300));
        set.add(new Person("Julia", 30, 100));
        set.add(new Person("Julia", 30, 100));

        System.out.println(set);

public static class Person implements Comparable<Person> {
        private int age;
        private String name;
        private int passportCode;


        public Person(String name, int age, int passportCode) {
            this.age = age;
            this.name = name;
            this.passportCode = passportCode;
        }


        @Override
        public boolean equals(Object obj) {
            boolean result = false;
            Person p = (Person)obj;
            if(p.passportCode == this.passportCode){
                result = true;
            }
            return result;
        }


        @Override
        public int compareTo(Person o) {
           if(this.passportCode < o.passportCode){
                return -1;
            } else if(this.passportCode > o.passportCode){
                return 1;
            } else {
                return 0;
            }
        }


        @Override
        public String toString() {
            return "Name: " + name + " age: " + age + " passportCode: " + passportCode +" ---- ";
        }
    }

[Name: Joe age: 33 passportCode: 400 ---- , Name: Julia age: 30 passportCode: 100 ---- , Name: Julia age: 30 passportCode: 100 ---- , Name: Kris age: 25 passportCode: 300 ---- ]

@Override
        public int hashCode() {
            return 0;
        }