73. Calculating the quarter of a given date

A year has 4 quarters (commonly denoted as Q1, Q2, Q3, and Q4) and each quarter has 3 months. If we consider that January is 0, February is 1, …, and December is 11, then we can observe that January/3 = 0, February/3 =0, March/3 = 0, and 0 can represent Q1. Next, 3/3 = 1, 4/3 = 1, 5/3 = 1, so 1 can represent Q2. Based on the same logic, 6/3 = 2, 7/3 = 2, 8/3 = 2, so 2 can represent Q3. Finally, 9/3 = 3, 10/3 = 3, 11/3 = 3, so 3 represents Q4.

Based on this statement and the Calendar API, we can obtain the following code:

public static String quarter(Date date) {
  String[] quarters = {"Q1", "Q2", "Q3", "Q4"};
  Calendar calendar = Calendar.getInstance();
  calendar.setTime(date);
  int quarter = calendar.get(Calendar.MONTH) / 3;
  return quarters[quarter];
}

But, starting with JDK 8, we can rely on java.time.temporal.IsoFields. This class contains fields (and units) that follow...