Java – why is the difference between specific dates (03 / 12 / 2018) not the exact number of days?

2020-08-21 • Java

I'm facing a strange problem with Java (versions 6, 7, 8) In this code, I try to calculate the date difference between two dates. This code gives my date difference between 03 / 12 / 2018 and 01 / 04 / 2018, which is 66.958 days instead of 67 days, which is a little surprising I haven't seen such behavior yet

To prove this theory, you can try any date before 03 / 11 / 2018, which is simple mathematics Please let us know what you think I've tried the chrononunit class bundled with Java, which correctly calculates the number of days, but I just want to know what happens here if you have any comments

static  void dateLogic1() throws ParseException{
       String matYear1 = "03/11/2018";
       String matYear2 = "03/12/2018";

       String stlDate = "01/04/2018";


       java.util.Date mtYear1 = new SimpleDateFormat("MM/dd/yyyy").parse(matYear1);
       java.util.Date mtYear2 = new SimpleDateFormat("MM/dd/yyyy").parse(matYear2);


       java.util.Date stYear = new SimpleDateFormat("MM/dd/yyyy").parse(stlDate);

       long time1 = mtYear1.getTime();
       long time2 = mtYear2.getTime();
       long time4 = stYear.getTime();


       double diff1 =  (double) (mtYear1.getTime()-stYear.getTime()) /( 24 * 60 * 60 * 1000);
       double diff2 =  (double) (mtYear2.getTime()-stYear.getTime()) /( 24 * 60 * 60 * 1000);

       System.out.println("Date Diff between "+ mtYear1 +" & "+ stYear +" is " + diff1 );
       System.out.println("Date Diff between "+ mtYear2  +" & "+ stYear +" is " + diff2 );

   }

Solution

It is related to daylight saving time At 2 a.m. on March 11, 2018, an hour was lost in many places If the hour is converted into a small part of the day (1 / 24), the result is a difference between 67 and 66.958

Edit: date Gettime() returns the number of milliseconds since 00:00:00 GMT, January 1, 1970, represented by the date object Because you lose one thousandth of an hour, that's the way fractional hours are lost

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