public void next(Knoop knoop) { @SuppressWarnings("unchecked") Enum<? extends Diagnose> diagnose = (Enum<? extends Diagnose>) knoop.getDiagnose(); Enum<? extends Diagnose>[] diagnoses = possibleDiagnoses().getEnumConstants(); knoop.setDiagnose((Diagnose) diagnoses[(diagnose.ordinal() + 1) % diagnoses.length]); }