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POCodeReview: java Dates diff (in day resolution)
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  1. POCodeReview: java Dates diff (in day resolution)
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    copied!<p>Please your opinion on the following code.</p> <p>I need to calculate the diff in days between 2 Date objects. It is assured that both Date objects are within the same TimeZone.</p> <pre><code>public class DateUtils { public final static long DAY_TIME_IN_MILLIS = 24 * 60 * 60 * 1000; /** * Compare between 2 dates in day resolution. * * @return positive integer if date1 &gt; date2, negative if date1 &lt; date2. 0 if they are equal. */ public static int datesDiffInDays(final Date date1, final Date date2){ long date1DaysMS = date1.getTime() - (date1.getTime() % DAY_TIME_IN_MILLIS); long date2DaysMS = date2.getTime() - (date2.getTime() % DAY_TIME_IN_MILLIS); long timeInMillisDiff = (date1DaysMS - date2DaysMS); int ret = (int) (timeInMillisDiff / DAY_TIME_IN_MILLIS); return ret; } </code></pre> <p>Can you point to a problem that I might have missed ?</p> <p>EDIT: @mmyers asked if pass my unit test. Well - Yes. But I have no real experience with dates and I know that is a big subject. Posted below the unit test that I'm using.</p> <pre><code>public class TestMLDateUtils { @Test public final void testDatesDiffInDays() { TimeZone.setDefault(TimeZone.getTimeZone("UTC")); // 00:00:00.000 1.1.1970 Calendar cal1970 = Calendar.getInstance(); cal1970.setTimeInMillis(0); Calendar tested = Calendar.getInstance(); tested.setTimeInMillis(0); // Add 1 millisecond, date = 00:00:00.001 1.1.1970 tested.add(Calendar.MILLISECOND, 1); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == 0); // Add 1 second, date = 00:00:01.001 1.1.1970 tested.add(Calendar.SECOND, 1); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == 0); // Add 1 minute, date = 00:01:01.001 1.1.1970 tested.add(Calendar.MINUTE, 1); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == 0); // Add 1 hour, date = 01:01:01.001 1.1.1970 tested.add(Calendar.HOUR_OF_DAY, 1); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == 0); // date = 23:59:59.999 1.1.1970 tested.setTimeInMillis(0); tested.add(Calendar.MILLISECOND, 999); tested.add(Calendar.SECOND, 59); tested.add(Calendar.MINUTE, 59); tested.add(Calendar.HOUR_OF_DAY, 23); //System.out.println("D: " + tested.getTime()); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == 0); // date = 00:00:00.000 2.1.1970 tested.setTimeInMillis(0); tested.add(Calendar.DAY_OF_MONTH, 1); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == -1); assertTrue(DateUtils.datesDiffInDays(tested.getTime(), cal1970.getTime()) == 1); // date = 00:00:00.001 2.1.1970 tested.add(Calendar.MILLISECOND, 1); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == -1); assertTrue(DateUtils.datesDiffInDays(tested.getTime(), cal1970.getTime()) == 1); // date = 00:00:01.001 2.1.1970 tested.add(Calendar.SECOND, 1); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == -1); assertTrue(DateUtils.datesDiffInDays(tested.getTime(), cal1970.getTime()) == 1); // date = 00:01:01.001 2.1.1970 tested.add(Calendar.MINUTE, 1); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == -1); assertTrue(DateUtils.datesDiffInDays(tested.getTime(), cal1970.getTime()) == 1); // date = 01:01:01.001 2.1.1970 tested.add(Calendar.HOUR_OF_DAY, 1); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == -1); assertTrue(DateUtils.datesDiffInDays(tested.getTime(), cal1970.getTime()) == 1); // date = 13:01:01.001 2.1.1970 tested.add(Calendar.HOUR_OF_DAY, 12); assertTrue(DateUtils.datesDiffInDays(cal1970.getTime(), tested.getTime()) == -1); assertTrue(DateUtils.datesDiffInDays(tested.getTime(), cal1970.getTime()) == 1); } } </code></pre>
 

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