Eclipse warning: "<methodName> has non-API return type <parameterizedType>"

Question

My co-worker and I have come across this warning message a couple times recently. For the below code:

package com.mycompany.product.data;

import com.mycompany.product.dao.GenericDAO;

public abstract class EntityBean {
    public abstract GenericDAO<Object, Long> getDAO();
    //                                       ^^^^^^      <-- WARNING OCCURS HERE
}

the warning appears in the listed spot as

EntityBean.getDAO() has non-API return type GenericDAO<T, ID>

A Google search for "has non-API return type" only shows instances where this message appears in problem lists. I.e., there's no public explanation for it.

What does this mean? We can create a usage problem filter in Eclipse to make the message go away, but we don't want to do this if our usage is a legitimate problem.

Thanks!

EDIT: This warning doesn't have to do with the parameterization, as this declaration of getFactory() also results in the same warning:

public abstract class EntityBean {
    protected DAOFactory getFactory() {
        return DAOFactory.instance(DAOFactory.HIBERNATE);
    }
}

Answer 1

Figured it out.

These classes (GenericDAO and DAOFactory as return types) and EntityBean were in different packages. One of the packages (the one containing EntityBean) was listed in the Export-Package: section of the manifest file, and the other package (DAOs) was not. The net effect is that the DAO classes were non-API and were being returned by an API type.

Thanks all, especially to JRL for orienting me in the right direction.