Question

I am working with the Java Calendar class to do the following:

1. Set a start date
2. Set an end date
3. Any date within that range is a “valid” date

I have this somewhat working, and somewhat not. Please see the code below:

    nowCalendar.set(Calendar.DATE, nowCalendar.get(Calendar.DATE) + offset);
    int nowDay = nowCalendar.get(Calendar.DATE);

    Calendar futureCalendar = Calendar.getInstance();
    futureCalendar.set(Calendar.DATE, nowDay + days);

    Date now = nowCalendar.getTime();
    Date endTime = futureCalendar.getTime();

    long now_ms = now.getTime();
    long endTime_ms = endTime.getTime();

    for (; now_ms < endTime_ms; now_ms += MILLIS_IN_DAY) {
        valid_days.addElement(new Date(now_ms));
        System.out.println("VALID DAY: " + new Date(now_ms));
    }

Basically, I set a “NOW” calendar and a “FUTURE” calendar, and then I compare the two calendars to find the valid days. On my calendar, valid days will be shaded white and invalid days will be shaded gray. You will notice two variables:

    offset = three days after the current selected date
    days = the number of valid days from the current selected date

This works…EXCEPT when the current selected date is the last day of the month, or two days prior (three all together). I think that its the offset that is definitely screwing it up, but the logic works everywhere else. Any ideas?

Answer 1

Don’t fiddle with milliseconds. Clone the nowCalendar, add 1 day to it using Calendar#add() in a loop as long as it does not exceed futureCalendar and get the Date out of it using Calendar#getTime().

Calendar clone = nowCalendar.clone();

while (!clone.after(futureCalendar)) {
    validDays.add(clone.getTime());
    clone.add(Calendar.DATE, 1);
}

(note that I improved validDays to be a List instead of the legacy Vector)