iso property
Returns an WeekYearRule consistent with ISO-8601.
In the standard ISO-8601 week algorithm, the first week of the year is that in which at least 4 days are in the year. As a result of this definition, day 1 of the first week may be in the previous year. In ISO-8601, weeks always begin on a Monday, so this rule is equivalent to the first Thursday being in the first Monday-to-Sunday week of the year.
For example, January 1st 2011 was a Saturday, so only two days of that week (Saturday and Sunday) were in 2011. Therefore January 1st is part of week 52 of week-year 2010. Conversely, December 31st 2012 is a Monday, so is part of week 1 of week-year 2013.
Implementation
static final WeekYearRule iso = SimpleWeekYearRule(4, DayOfWeek.monday, false);