Method between

base/src/main/java/net/time4j/CalendarUnit.java:680–744

(T start, T end)

        }

        @Override
        public long between(T start, T end) {

            PlainDate d1 = start.get(PlainDate.CALENDAR_DATE);
            PlainDate d2 = end.get(PlainDate.CALENDAR_DATE);
            long amount;

            switch (this.unit) {
                case MILLENNIA:
                    amount = this.monthDelta(d1, d2) / 12000;
                    break;
                case CENTURIES:
                    amount = this.monthDelta(d1, d2) / 1200;
                    break;
                case DECADES:
                    amount = this.monthDelta(d1, d2) / 120;
                    break;
                case YEARS:
                    amount = this.monthDelta(d1, d2) / 12;
                    break;
                case QUARTERS:
                    amount = this.monthDelta(d1, d2) / 3;
                    break;
                case MONTHS:
                    amount = this.monthDelta(d1, d2);
                    break;
                case WEEKS:
                    amount = dayDelta(d1, d2) / 7;
                    break;
                case DAYS:
                    amount = dayDelta(d1, d2);
                    break;
                default:
                    throw new UnsupportedOperationException(this.unit.name());
            }

            if (
                (amount != 0)
                && start.contains(PlainTime.WALL_TIME)
                && end.contains(PlainTime.WALL_TIME)
            ) {
                boolean needsTimeCorrection;

                if (this.unit == DAYS) {
                    needsTimeCorrection = true;
                } else {
                    PlainDate d = d1.plus(amount, this.unit);
                    needsTimeCorrection = (d.compareByTime(d2) == 0);
                }

                if (needsTimeCorrection) {
                    PlainTime t1 = start.get(PlainTime.WALL_TIME);
                    PlainTime t2 = end.get(PlainTime.WALL_TIME);

                    if ((amount > 0) && t1.isAfter(t2)) {
                        amount--;
                    } else if ((amount < 0) && t1.isBefore(t2)) {
                        amount++;