Логика чтения/записи реализованная в методах save/load должна работать корректно в случае, если список users не пустой.

package com.javarush.task.task20.task2002;

import java.io.*;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

/*
Читаем и пишем в файл: JavaRush
*/
public class Solution {
    public static void main(String[] args) {
        //you can find your_file_name.tmp in your TMP directory or fix outputStream/inputStream according to your real file location
        //вы можете найти your_file_name.tmp в папке TMP или исправьте outputStream/inputStream в соответствии с путем к вашему реальному файлу
        try {
            File your_file_name = File.createTempFile("your_file_name", null);
            OutputStream outputStream = new FileOutputStream(your_file_name);
            InputStream inputStream = new FileInputStream(your_file_name);

            JavaRush javaRush = new JavaRush();
            User a = new User();
            a.setFirstName("Oleg");
            a.setLastName("Kuchik");
            a.setBirthDate(new Date());
            a.setCountry(User.Country.UKRAINE);
            a.setMale(true);
            javaRush.users.add(a);

            //initialize users field for the javaRush object here - инициализируйте поле users для объекта javaRush тут
            javaRush.save(outputStream);
            outputStream.flush();

            JavaRush loadedObject = new JavaRush();
            loadedObject.load(inputStream);
            System.out.println(javaRush.equals(loadedObject));
            //check here that javaRush object equals to loadedObject object - проверьте тут, что javaRush и loadedObject равны

            outputStream.close();
            inputStream.close();

        } catch (IOException e) {
            //e.printStackTrace();
            System.out.println("Oops, something wrong with my file");
        } catch (Exception e) {
            //e.printStackTrace();
            System.out.println("Oops, something wrong with save/load method");
        }
    }

    public static class JavaRush {
        public List<User> users = new ArrayList<>();

        public void save(OutputStream outputStream) throws Exception {
            for (int i = 0; i < users.size(); i++) {
                String isUserPresent = users.get(i) != null ? "yes" : "no";
                PrintWriter printWriter = new PrintWriter(outputStream);
                printWriter.println(isUserPresent);
                if (isUserPresent.equals("yes"))
                {
                    printWriter.println(users.get(i).getFirstName());
                    printWriter.println(users.get(i).getLastName());
                    printWriter.println(users.get(i).getCountry().getDisplayedName());
                    printWriter.println(users.get(i).getBirthDate().getTime());
                    printWriter.println(users.get(i).isMale());
                }
                printWriter.flush();
                printWriter.close();
            }
            //implement this method - реализуйте этот метод
        }

        public void load(InputStream inputStream) throws Exception {
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
            ArrayList<User> users = new ArrayList<>();
            while (reader.ready()) {
                String s = reader.readLine();
                String[] w = s.split(" ");
                User human = new User();
                if (w[0] != null)
                    human.setFirstName(w[0]);
                if (w[1] != null)
                    human.setLastName(w[1]);
                if (w[2] != null) {

                    if (w[2].equals("true"))
                        human.setMale(true);
                    else human.setMale(false);
                }





                if (w[3] != null)
                    human.setBirthDate(new Date(Long.parseLong(w[3])));
                if (w[4] != null)
                {
                    human.setCountry(User.Country.valueOf(w[4]));
                }
                users.add(human);
            }
            reader.close();

            //implement this method - реализуйте этот метод
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            JavaRush javaRush = (JavaRush) o;

            return users != null ? users.equals(javaRush.users) : javaRush.users == null;

        }

        @Override
        public int hashCode() {
            return users != null ? users.hashCode() : 0;
        }
    }
}




package com.javarush.task.task20.task2002;

import java.util.Date;

public class User {
    private String firstName;
    private String lastName;
    private Date birthDate;
    private boolean isMale;
    private Country country;

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public Date getBirthDate() {
        return birthDate;
    }

    public void setBirthDate(Date birthDate) {
        this.birthDate = birthDate;
    }

    public boolean isMale() {
        return isMale;
    }

    public void setMale(boolean male) {
        isMale = male;
    }

    public Country getCountry() {
        return country;
    }

    public void setCountry(Country country) {
        this.country = country;
    }

    public void setBirthDate(long time) {

    }

    public static enum Country {
        UKRAINE("Ukraine"),
        RUSSIA("Russia"),
        OTHER("Other");

        private String name;

        private Country(String name) {
            this.name = name;
        }

        public String getDisplayedName() {
            return this.name;
        }
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        User user = (User) o;

        if (isMale != user.isMale) return false;
        if (firstName != null ? !firstName.equals(user.firstName) : user.firstName != null) return false;
        if (lastName != null ? !lastName.equals(user.lastName) : user.lastName != null) return false;
        if (birthDate != null ? !birthDate.equals(user.birthDate) : user.birthDate != null) return false;
        return country == user.country;

    }

    @Override
    public int hashCode() {
        int result = firstName != null ? firstName.hashCode() : 0;
        result = 31 * result + (lastName != null ? lastName.hashCode() : 0);
        result = 31 * result + (birthDate != null ? birthDate.hashCode() : 0);
        result = 31 * result + (isMale ? 1 : 0);
        result = 31 * result + (country != null ? country.hashCode() : 0);
        return result;
    }
}