Generic type as a constructor parameter

Question

I have a generic dao interface implemented like this:

public interface GenericDao<T extends AbstractEntity> 

and AbstractHibernateDao class:

public abstract class AbstractHibernateDao<T extends AbstractEntity> implements GenericDao<T> 

I'm trying to make generic table model like this:

public class EntityTableModel extends DefaultTableModel {

private GenericDao<AbstractEntity> dao;

public EntityTableModel(GenericDao<AbstractEntity> dao, String[] columnLabels) {
    super(columnLabels, 0);
    this.dao = dao;
}

The way I tried to pass a parameter looks like this:

table.setModel(new EntityTableModel(new SomeEntityHibernateDao(),columns));enter code here

And code for SomeEntityHibernateDao looks like this:

public class SomeEntityHibernateDao extends AbstractHibernateDao<SomeEntity> implements
    SomeEntityDao

SomeEntity extends AbstractEntity and SomeEntityDao is interface which extends GenericDao interface.

Can somebody explain to me why this isn't working? Any help would be really appreciated.

Answer 1

GenericDao<SomeSpecificEntity> is not the same as GenericDao<AbstractEntity>.

Instead, you should allow subclasses:

GenericDao<? extends AbstractEntity> 

You will not be able to call any methods on it that accept T as a parameter, since you don't know what T is.

Alternatively, you could make the entire TableModel class generic, and accept a GenericDao<T>.