Hashcode.java

    class User {

        String email;

        int age;

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

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