android sqllite cannot be accessed from outside package

I am making an Android app to learn sqllite. Because I use 7 tables, I decided to create 7 class files in a folder "DBHelper", and want to make 7 files in a folder "DBadapter". Here what the structure looks like:

root

• DBHelper: 7 helper files (ex: PersonHelper.java)
• DBadapter: 7 adapter files (ex: PersonDAO.java)

But I get an error message with PersonDAO.java: "cannot be accessed from outside package", when I declared the object: "PersonHelper personHelper = new PersonHelper(context);" in the constructor.

Anyone has an idea how to fix that without putting all files in one folder? What is the standard in the industry when creating multiple large tables?

PS: The error is gone once I place all files in one directory.

public class PersonDAO {
private Context context;

//Database info
private static final String DATABASE_NAME = "MyDB";
private static final int DATABASE_VERSION = 1;

//Table helper info
public PersonHelper databaseHelper;
private SQLiteDatabase db = null;


//Constructors
PersonDAO(Context context) {
    this.context = context;
    databaseHelper = new PersonHelper(context); //Error: "cannot be accessed from outside package"
}