Generics compiler error

[Bob Sturim]

I'm using generics in a simple class. I'm getting a compile time error and for the life of me, I can't figure it out. Any held would be appreciated. My class is:

public class DB {
    private static final Map<Class<? extends BaseDTO>, ? extends Map<Long, ? extends BaseDTO>> db      = new HashMap<Class<? extends BaseDTO>, Map<Long, ? extends BaseDTO>>();
 

    /**
     * @param entity
     */
    public static <T extends BaseDTO> void merge(T entity) {
        synchronized (db) {
            Map<Long, ? extends BaseDTO> map = db.get(entity.getClass());
            if (map == null) {
                map = new TreeMap<Long, T>();
                db.put(entity.getClass(), map);
            }
            entity.setId(counter++);
            map.put(entity.getId(), entity);
        }
    }
    long counter = 0;
}
 

BaseDTO is a base class which, for the purposes of this discussions, contains a single property, Long id.

The compiler complains at the two put statements:

The method put(Class<? extends BaseDTO>, capture-of ? extends Map<Long,? extends BaseDTO> :wink:  in the type Map<Class<? extends BaseDTO>,capture-of ? extends Map<Long,? extends BaseDTO>> is not applicable for the arguments (Class<capture-of ? extends BaseDTO>, Map<Long,capture-of ? extends BaseDTO> :wink: DB.java

Thanks!