Add 1 Week to a Date, which way is preferred?

Asked 2010-07-21T14:29:38.187

I am reviewing some code at work and came across an inconsistency in how the code handles adding 1 week to the current time and was wondering if there was any reason why one should really be preferred over the other:

The first was a utility method:

public static Date addDaysToDate(final Date date, int noOfDays) {
    Date newDate = new Date(date.getTime());

    GregorianCalendar calendar = new GregorianCalendar();
    calendar.setTime(newDate);
    calendar.add(Calendar.DATE, noOfDays);
    newDate.setTime(calendar.getTime().getTime());

    return newDate;
}

And the second used simple millisecond arithmetic:

long theFuture = System.currentTimeMillis() + (86400 * 7 * 1000);
Date nextWeek = new Date(theFuture);

The second method obviously uses 'magic numbers' to define a week, but this could be moved to a constant MILLISECONDS_IN_ONE_WEEK = 86400 * 7 * 1000 So other than that, is there any reasons why one of these methods should be preferred over the other?

Basically I want to change the code to be consistent throughout, but I'm not entirely sure which one to remove. So any arguments one way or the other would be useful.

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2 Answers

First and foremost, I would argue that you replace it with JodaTime. http://joda-time.sourceforge.net/ It is a very nice time library. You'll want to look at this page to see how easy it is to add days or weeks to a particular point in time: http://joda-time.sourceforge.net/key_period.html Can't do this, mobile device with incompatible JVM. Bummer.

Your first example is easier to read and will be easier to use by your developers. It also uses the Calendar classes which is the generally accepted way to manipulate dates in Java. What makes it better is that it has a clear method name that sets the expectation for what it does.

So if you refactor your system to consistently use com.DaveJ.util.date.DateUtils.addDaysToDate(final Date date, int noOfDays) you can then do whatever you want inside that method, be it Calendar or millis or Joda, and be consistent within your application. Don't forget to write some unit tests for it!

answered 2010-07-21T14:38:33.467

The first will be slower, so if performance is an issue, the second one is better.

answered 2010-07-21T14:37:40.097

Add 1 Week to a Date, which way is preferred?

2 Answers

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