@ManyToMany
@JoinTable(
    name = "user_role",
    joinColumns = @JoinColumn(name = "user_id"),
    inverseJoinColumns = @JoinColumn(name = "role_id")
)
private Set<Role> roles;

@ElementCollection
@CollectionTable(
    name = "phone_numbers",
    joinColumns = @JoinColumn(name = "user_id"),
    uniqueConstraints = @UniqueConstraint(columnNames = {"user_id", "phone_number"}),
    indexes = @Index(columnList = "phone_number")
)
@Column(name = "phone_number")
private Set<String> phoneNumbers;

import java.util.HashMap;

public class Task170325 {
    public static void main(String[] args) {
        HashMap<String, Integer> map = new HashMap<>();
        map.put(new String("a"), 1);
        map.put(new String("a"), 2);

        System.out.println(map.size());
    }
}

@ElementCollection
@OrderColumn(name = "item_order")
private List<String> items;

@ElementCollection
@CollectionTable(name = "items", joinColumns = @JoinColumn(name = "user_id"))
@OrderColumn(name = "item_order", columnDefinition = "INT NOT NULL")
private List<String> items;

@Entity
@PrimaryKeyJoinColumn(name = "employee_id", referencedColumnName = "id")
public class Employee extends Person {
    // Дополнительные поля и методы
}

@Entity
@PrimaryKeyJoinColumn(
    name = "employee_id",
    referencedColumnName = "id",
    foreignKey = @ForeignKey(name = "fk_employee_person")
)
public class Employee extends Person {
    // Дополнительные поля и методы
}