Android java房间数据库，app构建错误

// User.java
@Entity(tableName = "users")
public class User {
    @PrimaryKey(autoGenerate = true)
    public int id;

    @ColumnInfo(name = "first_name")
    public String firstName;

    @ColumnInfo(name = "last_name")
    public String lastName;
}

// UserDao.java
@Dao
public interface UserDao {
    @Query("SELECT * FROM users")
    List<User> getAll();

    @Insert
    void insertAll(User... users);

    @Delete
    void delete(User user);
}

// AppDatabase.java
@Database(entities = {User.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {
    public abstract UserDao userDao();
}

// MainActivity.java
public class MainActivity extends AppCompatActivity {
    private AppDatabase db;
    private UserDao userDao;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        db = Room.databaseBuilder(getApplicationContext(),
                AppDatabase.class, "database-name").build();
        userDao = db.userDao();

        User user = new User();
        user.firstName = "John";
        user.lastName = "Doe";

        new Thread(new Runnable() {
            @Override
            public void run() {
                userDao.insertAll(user);
            }
        }).start();
    }
}