equals, hashCode, Comparable

public final class User implements Comparable<User> {
    private final long id;
    private final String email;

    public User(long id, String email) {
        this.id = id;
        this.email = email;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (!(obj instanceof User other)) return false;
        return id == other.id && Objects.equals(email, other.email);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, email);
    }

    @Override
    public int compareTo(User other) {
        return Long.compare(this.id, other.id);
    }
}