new Comparator<HealthCheckPosition>(){
    @Override
    public int compare(HealthCheckPosition o1, HealthCheckPosition o2) {
        return DateTimeComparator.getDateOnlyInstance().compare(o1.getInstrument().getRelevantExpirationDate(), o2.getInstrument().getRelevantExpirationDate());
    }
};
   

Als Lambda:

(Comparator<HealthCheckPosition>) (o1, o2) -> DateTimeComparator.getDateOnlyInstance().compare(o1.getInstrument().getRelevantExpirationDate(), o2.getInstrument().getRelevantExpirationDate());