public class SxxxxxxZ3{

     public static void main(String [] args){

        Person kowalski = new Person("Jan", "Kowalski", 20);
        Student pierwszy = new Student(kowalski);
        pierwszy.setFieldOfStudy("Matematyka");

        Person nowak = new Person ("Karol", "Nowak", 22);
        Student drugi = new Student(nowak);
        drugi.setFieldOfStudy("Fizyka");
        drugi.completeSemester();

        System.out.println("Student 1: " + pierwszy + "\nStudent 2: " + drugi);
     }
}

class Person
{
    private String name;
    private String surname;
    private int age;

    public Person()
    {
    }

    public String toString()
    {
        return "Name: " + name + ", Surname: " + surname + ", Age: " + age;
    }
}

interface StudentIDSetting
{
    public void setStudentID(int id);
}

class Student implements StudentIDSetting
{
    private Person person;
    private int studentID;
    private String fieldOfStudy;
    private boolean semesterCompleted = false;

    // Wartość wspólna dla wszystkich obiektów tej klasy
    static private int nextStudentID = 0;

    public Student(Person person)
    {
        this.person = person;

        studentID = nextStudentID;
        ++nextStudentID; //następny utworzony obiekt klasy Student będzie miał studentID o 1 większe
    }
    public void setStudentID(int id)
    {
        studentID = id;
    }

    public void setFieldOfStudy(String field)
    {
        this.fieldOfStudy = field;
    }
    public String getFieldOfStudy()
    {
        return fieldOfStudy;
    }
    public void completeSemester()
    {
        semesterCompleted = true;
    }
    public String toString()
    {
        return person + ", Student ID: " + studentID + ", Field of Study: " + fieldOfStudy + ", Semester Completed: " + (semesterCompleted ? "YES" : "NO");
    }
}