coursera-ibm-java-developer-course/PetCareScheduler/src/main/java/Pet.java

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import static java.util.Objects.requireNonNull;

public final class Pet {

    private String id;
    private String name;
    private String owner;
    private String contactInformation;
    private String breed;
    private int age;
    private LocalDate registrationDate;
    private final List<Appointment> appointments = new ArrayList<>();

    public Pet(String id, String name, String owner, String contactInformation, String breed, int age, LocalDate registrationDate) {

        if (age < 0) throw new IllegalArgumentException("Age must be over 0");

        this.age = age;
        this.id = requireNonNull(id, "id must not be null");
        this.name = requireNonNull(name, "Name must not be null");
        this.owner = requireNonNull(owner, "Owner must not be null");
        this.contactInformation = requireNonNull(contactInformation, "Contact information must not be null");
        this.breed = requireNonNull(breed, "Breed must not be null");
        this.registrationDate = requireNonNull(registrationDate, "Registration date must not be null");
    }

    public void addAppointment(Appointment appointment) {
        this.appointments.add(requireNonNull(appointment, "Appointment must not be null"));
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getOwner() {
        return owner;
    }

    public String getContactInformation() {
        return contactInformation;
    }

    public String getBreed() {
        return breed;
    }

    public int getAge() {
        return age;
    }

    public LocalDate getRegistrationDate() {
        return registrationDate;
    }

    public List<Appointment> getAppointments() {
        return Collections.unmodifiableList(appointments);
    }

    public void setId(String id) {
        this.id = requireNonNull(id, "id must not be null");
    }

    public void setName(String name) {
        this.name = requireNonNull(name, "Name must not be null");
    }

    public void setOwner(String owner) {
        this.owner = requireNonNull(owner, "Owner must not be null");
    }

    public void setContactInformation(String contactInformation) {
        this.contactInformation =requireNonNull(contactInformation, "Contact information must not be null");
    }

    public void setBreed(String breed) {
        this.breed = requireNonNull(breed, "Breed must not be null");
    }

    public void setAge(int age) {
        if (age < 0) throw new IllegalArgumentException("Age must be over 0");
        this.age = age;
    }

    public void setRegistrationDate(LocalDate registrationDate) {
        this.registrationDate = requireNonNull(registrationDate, "Registration date must not be null");
    }

    @Override
    public String toString() {
        return "Pet{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", owner='" + owner + '\'' +
                ", contactInformation='" + contactInformation + '\'' +
                ", breed='" + breed + '\'' +
                ", age=" + age +
                ", registrationDate=" + registrationDate +
                ", appointments=" + appointments +
                '}';
    }
}