抽象类 - 扩展类和DAO

Question

I have a abstract class User and 3 classes who extend from this class (Admin, Modurator, Lector).

In my db I have a table User with the data needed (UserName / Password / Security_lvl).

The connection to the database for User I do with DAO.

public class MysqlUserDao implements UserDao {
    //
    private static MysqlUserDao instance;

    //
    public static MysqlUserDao getInstance() {
        if (instance == null)
            instance = new MysqlUserDao();
        return instance;
    }
public void create(User user) {
        try {
            c = MySqlDAOFactory.getInstance().getConnection();
            //
            String sql = "insert into user values (?,?,?)";
            //
            prest = c.prepareStatement(sql);
            //
            prest.setString(1, user.getUserName());
            prest.setString(2, user.getPassword());
            prest.setInt(3, user.getRole().returnSecurityLevel());
            //
            prest.executeUpdate();
            //
        } catch (SQLException e) {
            JdbcLogging.info("error item" + " :"
                    + e);
        } finally {
            MySqlConnectionFactory.getInstance().closeResultSet(rs);
            MySqlConnectionFactory.getInstance().closeStatement(prest);
            MySqlConnectionFactory.getInstance().closeConnection(c);
        }
    }

}

In java depending on the user-type I make the specific Admin, Modurator or Lector objects so I can use their specific methods.

Now the problem I have, is that I need a User for this DAO. But User is abstract and I do not make any User objects. I can make three different DAO's for each of the other classes but they would just do the same. Is there a clean way to do this ... .

Their maybe is a simple solution but I'm just not seeing it.

Answer 1

You can pass Admin, Moderator or Lector instances as parameters to your create method. Polymorphism in Java allows that kind of behaviour.