in src/main/java/org/apache/commons/lang3/time/DateUtils.java [968:1038]
public static Iterator<Calendar> iterator(final Calendar calendar, final int rangeStyle) {
Objects.requireNonNull(calendar, "calendar");
final Calendar start;
final Calendar end;
int startCutoff = Calendar.SUNDAY;
int endCutoff = Calendar.SATURDAY;
switch (rangeStyle) {
case RANGE_MONTH_SUNDAY:
case RANGE_MONTH_MONDAY:
//Set start to the first of the month
start = truncate(calendar, Calendar.MONTH);
//Set end to the last of the month
end = (Calendar) start.clone();
end.add(Calendar.MONTH, 1);
end.add(Calendar.DATE, -1);
//Loop start back to the previous sunday or monday
if (rangeStyle == RANGE_MONTH_MONDAY) {
startCutoff = Calendar.MONDAY;
endCutoff = Calendar.SUNDAY;
}
break;
case RANGE_WEEK_SUNDAY:
case RANGE_WEEK_MONDAY:
case RANGE_WEEK_RELATIVE:
case RANGE_WEEK_CENTER:
//Set start and end to the current date
start = truncate(calendar, Calendar.DATE);
end = truncate(calendar, Calendar.DATE);
switch (rangeStyle) {
case RANGE_WEEK_SUNDAY:
//already set by default
break;
case RANGE_WEEK_MONDAY:
startCutoff = Calendar.MONDAY;
endCutoff = Calendar.SUNDAY;
break;
case RANGE_WEEK_RELATIVE:
startCutoff = calendar.get(Calendar.DAY_OF_WEEK);
endCutoff = startCutoff - 1;
break;
case RANGE_WEEK_CENTER:
startCutoff = calendar.get(Calendar.DAY_OF_WEEK) - 3;
endCutoff = calendar.get(Calendar.DAY_OF_WEEK) + 3;
break;
default:
break;
}
break;
default:
throw new IllegalArgumentException("The range style " + rangeStyle + " is not valid.");
}
if (startCutoff < Calendar.SUNDAY) {
startCutoff += 7;
}
if (startCutoff > Calendar.SATURDAY) {
startCutoff -= 7;
}
if (endCutoff < Calendar.SUNDAY) {
endCutoff += 7;
}
if (endCutoff > Calendar.SATURDAY) {
endCutoff -= 7;
}
while (start.get(Calendar.DAY_OF_WEEK) != startCutoff) {
start.add(Calendar.DATE, -1);
}
while (end.get(Calendar.DAY_OF_WEEK) != endCutoff) {
end.add(Calendar.DATE, 1);
}
return new DateIterator(start, end);
}