为什么这样设计Dao？

public interface BaseDAO {



    public void save(Object obj);	

    public void update(Object obj);

    public void saveOrUpdate(Object obj);

	public void delete(Object obj) ;

	public void executeHQL(String hql,Object obj);

	public Object findById(Class clazz,Integer id);

	

	/**

	 * 

	 * @param shortClassName    entity bean的类名，省去包名   

	 * @param id

	 * @return

	 */

		

	public Object findById(String shortClassName,Integer id);

	public List findAll(String shortClassName);

	public List findByParam(String hql,Object obj);

	public int calculateAmount(final Class clazz,final Map conditions);

	

	/**

	 * 该方法应用于查询分页

	 * 

	 * @param clazz       待查询的类

	 * @param conditions  条件组合

	 * @param orderType   排序方式

	 * @param orderField  按哪个属性进行排序

	 * @param start       开始位置    

	 * @param pageSize    返回的页大小

	 * @return

	 */

	public List filter(final Class clazz,final Map conditions, final String orderType,final String orderField,final int start,final int pageSize);

   

}

  public interface UserDAO extends BaseDAO{

	

	

	public static final String FIND_USER_BY_LOGIN_NAME = " from User u where u.loginName=?";

	

	public static final String DEL_USER_BY_ID = " delete from User u where u.id=?";

	

	public void addUser(User user) ;

	

	

	public void updateUser(User user) ;

	

	

	public void delUser(User user) ;

	

	

	public void delUserById(final int userid);

	

	

	public User findUserById(int id);

	

	

	public User findUserByLoginName(String loginName);



}

public class UserDAOHibernate  extends BaseDAOHibernate implements UserDAO{

	

	public void addUser(User user) {

		save(user);

	}

	

	public void updateUser(User user) {

		update(user);

	}

	

	public void delUser(User user) {

		delete(user);

	}

	

	public void delUserById(final int userid){

		

		getHibernateTemplate().execute(new HibernateCallback() {

			public Object doInHibernate(Session s) throws HibernateException, SQLException {

				Query query = s.createQuery(DEL_USER_BY_ID);

				query.setInteger(0, userid);

				query.executeUpdate();

				return null;

			}

		});

	}

	

	public User findUserById(int id){

		return (User)findById("User",id);

	}

	

	

	public User findUserByLoginName(String loginName){

		List list = this.getHibernateTemplate().find(FIND_USER_BY_LOGIN_NAME, loginName);

		if (list.size()>0) 

			return (User)list.get(0);

		return null;

	}	



}