Question

I am working on a project that will run many thousands of comparisons between dates to see if they are in the same month, and I am wondering what the most efficient way of doing it would be.

This isn’t exactly what my code looks like, but here’s the gist:

List<Date> dates = getABunchOfDates();
Calendar month = Calendar.getInstance();
for(int i = 0; i < numMonths; i++) 
{
    for(Date date : dates)
    {
        if(sameMonth(month, date)
            .. doSomething
    }
    month.add(Calendar.MONTH, -1);
}

Creating a new Calendar object for every date seems like a pretty hefty overhead when this comparison will happen thousands of times, soI kind of want to cheat a bit and use the deprecated method Date.getMonth() and Date.getYear()

public static boolean sameMonth(Calendar month, Date date)
{
    return month.get(Calendar.YEAR) == date.getYear() && month.get(Calendar.MONTH) == date.getMonth();
}

I’m pretty close to just using this method, since it seems to be the fastest, but is there a faster way? And is this a foolish way, since the Date methods are deprecated? Note: This project will always run with Java 7

Answer 1

I can’t comment on whether to use the deprecated methods, but if you choose not to there’s no need to instantiate a new Calendar for every Date you check. Just use one other Calendar and call setTime(date) before the check (or one Calendar for every thread if you parallelize it).

As a side note, I do have to agree with ChristopheD’s comment that this is something worthy of a database.