Get all Fridays in a date Range in Java

Question

I recently came across a task where i have to get all Fridays in a date range. I wrote a small piece of code and was surprised see some strange behaviour.

Below is m

Answer 1

First off, I would not bother with weeks. Set the Calendar to the beginning of the range, and figure out which DOW it is, then increment to get to the next Friday, then simply loop adding 7 days until you are at the end of the range.

Actually, since you are always only going forward, should be something like:

int daysToAdd = FridayDOW - currentDOW;
if (daysToAdd < 0) daysToAdd += 7; 
Date startDate = currentDate.add(Calendar.DAYS, daysToAdd);

Yeah, like that.

Ok, actually, for kicks, here it is in Java 8:

@Test
public void canFindAllFridaysInRange(){
    start = LocalDate.of(2013, 5, 10);
    end = LocalDate.of(2013, 8,30);

    DayOfWeek dowOfStart = start.getDayOfWeek();
    int difference = DayOfWeek.FRIDAY.getValue() - dowOfStart.getValue();
    if (difference < 0) difference += 7;

    List fridaysInRange = new ArrayList();

    LocalDate currentFriday = start.plusDays(difference);
    do {
        fridaysInRange.add(currentFriday);
        currentFriday = currentFriday.plusDays(7);
    } while (currentFriday.isBefore(end));

    System.out.println("Fridays in range: " + fridaysInRange);
}

Got to love the new date classes!! Of course a lambda would condense this further.