Main

package org.example;
import java.util.ArrayList;
import java.util.*;

public class Main {

    public static void main(String[] args) {

        Person firstPerson = new Person("Mariia", 19);
        Person secondPerson = new Person("Nikolas",24);
        Person thirdPerson = new Person("Elvira",20);
        Person fourthPerson = new Person("Olya",21);
        Person fifthPerson = new Person("Kate",22);

        Student firstStudent = new Student("Oleh", 20, 3, "standard");
        Student secondStudent = new Student("Olena", 18, 4, "increased");
        Student thirdStudent = new Student("Mikhail",22, 4, "increased");
        Student fourthStudent = new Student("Alex",21, 2, "standard");
        Student fifthStudent = new Student("Nikola",27, 2, "standard");

        ArrayList<Person> personArrayList = new ArrayList<Person>();
        personArrayList.add(firstPerson);
        personArrayList.add(secondPerson);
        personArrayList.add(thirdPerson);
        personArrayList.add(fourthPerson);
        personArrayList.add(fifthPerson);

        personArrayList.add(firstStudent);
        personArrayList.add(secondStudent);
        personArrayList.add(thirdStudent);
        personArrayList.add(fourthStudent);
        personArrayList.add(fifthStudent);

        for (int i = 0; i < personArrayList.size(); i++){
            System.out.println(personArrayList.get(i));
        }

        Comparator<Person> ageComp = new Comparator<Person>() {
            @Override
            public int compare(Person firstPerson, Person secondPerson) {
                Objects.requireNonNull(firstPerson);
                Objects.requireNonNull(secondPerson);

                if(firstPerson.getAge == secondPerson.getAge()) {
                    return 0;
                } else if (firstPerson.getAge > secondPerson.getAge()){
                    return -1;
                } else {
                    return 1;
                }
            }
        };

        System.out.println("------------------------------------------------------");
        System.out.println("Age sorting:");

        personArrayList.sort(ageComp);
        for (int i = 0; i < personArrayList.size(); i++){
            System.out.println(personArrayList.get(i));
        }
    }
}