@ManyToOne
@JoinColumn(name = "user_id", referencedColumnName = "id", nullable = false)
private User user;

import java.util.TreeMap;

public class Task140325 {
    public static void main(String[] args) {
        TreeMap<Integer, String> map = new TreeMap<>();
        map.put(5, "Five");
        map.put(2, "Two");
        map.put(8, "Eight");
        map.put(1, "One");
        System.out.println(map.higherKey(2) + map.lowerKey(5));
    }
}

@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());
    }
}