public List extends Comment> getComments() throws RemoteException; public List getComments(int questionnaireId) throws RemoteException { return classLoader.getQuestionnaire(questionnaireId).getComments(); The compiler issues a Type mismatch: cannot convert from List to List Which I find perplexing as the compiler can assure that at the very least it is a List of Comment objects. Yes, however Java's generics work correctly to prevent you ...