Question

Here is a class I have :

public class ProxyDAO<T extends DAO<? extends Model>> implements DAO<? extends Model> {
   ...
}

The compiler complains that A supertype may not implement a wildcard.

I have tried this:

public class ProxyDAO<T extends DAO<? extends Model>> implements DAO<Model> {
   ...
}

But subclasses of Model are now not allowed.

How can I tell the compiler that ProxyDAO implements the DAO interface and that this interface would be accept a Model class or any subclasses or Model ?

DAO.java

public interface DAO<T extends Model> {
    T findByPK(Object pk);
}

Answer 1

Use the following:

public class ProxyDAO<T extends Model> implements DAO<T>

And if you need to allow for supclasses of DAO:

public class ProxyDAO<T extends Model, V extends DAO<T>> implements DAO<T>