generics - cast problem

[jerzy burzek]

Zdravim konferenciu, skusam sa hrat s generics a narazilo som na jeden problem, ktoremu velmi nerozumiem. Skusim nacrtnut: mam hierarchiu tried (JPA, ale to nie je asi podstatne) BaseEntity ZipCode extends BaseEntity Login extends BaseEntity atd potom mam abstraktnu triedu BaseManager, ktora implementuje metodu pre nacitanie kolekcie z databazy: protected Collection loadCollectionByQuery(Class entityClass, String query, Object[] params) throws DBException..... a dalsiu triedu LOVManager, a tu mam metodu public Collection getAllZipCodes() throws DBException a tu je problem: ak napisem nieco taketo: public Collection getAllZipCodes() throws DBException     return (Collection) loadCollectionByQuery(ZipCode.class, "select z from ZipCode z", null); }       prekladac hlasi warning (unchecked cast...), a ked si vypisem po caste hodnoty v kolekcii, su tam instancie ZipCode, ale hodnoty atributov id a stamp (ktore su v BaseEntity) su null (???) ked naspisem toto: public Collection getAllZipCodes() throws DBException         Collection tmp = loadCollectionByQuery(ZipCode.class, "select z from ZipCode z", null);         Collection ret = (Collection) tmp;         return tmp; }       prekladac sice tiez hlasi warning, ale instancie ZipCode su uz ok (id aj stamp su != null) Co mi unika?