readAndSaveActiveSubUnits(subUnit, allActiveSubUnits, currentDate);
if (subUnit.isActive(currentDate)) { allActiveSubUnits.add(subUnit); }
    public List<Unit> getActiveSubUnits(Date currentDate) {        Set<Unit> allActiveSubUnits = new HashSet<Unit>();        for (Unit subUnit : this.getSubUnits()) {            readAndSaveActiveSubUnits(subUnit, allActiveSubUnits, currentDate);        }        return new ArrayList<Unit>(allActiveSubUnits);    }