calculating number of days between dates

Question

I'm aware of calculating number of days between two dates.

Java, Calculate the number of days between two dates

But i'm not able to understand how the calculation is made in below piece of code. Particularly the one which is highlighted below.

return (int)( (d2.getTime() - d1.getTime()) / (1000*60*60*24));

Kindly let me know the logic behind this.

Answer 1

The question you have linked has an answer from Jon Skeet. You should consider that. For your code, the difference between two dates is being returned in Millisecond. To convert into a single day the calculation is:

(1000       *    60     *  60     *    24));
 millisecond  seconds    minutes    hours in day ==> One day

Answer 2

The time is represented as millisecond, so you have 24 * 60 * 60 * 1000 because

24 * there are 24 hours in a day
60 * there are 60 minutes in an hour
60 * there are 60 seconds in a minute
1000 * there are 1000 milliseconds in a second

Answer 3

Dude getTime() method gives you time in milliseconds. So diffrence would be millis only then you try to covert it into seconds by dividing it by 1000 then to minutes by dividing it by 60 then to hours then to days (1 day is 24 hrs).

I hope you get it.

Answer 4

Method getTime() returns the number of milliseconds since January 1, 1970, 00:00:00 GMT represented by this Date object as stated in:

http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Date.html

And I believe I don't even have to describe the rest as this is the only thing that might be unclear to you ;)

Answer 5

This is pretty straight.

1. (d2.getTime() - d1.getTime()) gives you diference no. of milli seconds between two dates.

2. 1000 * 60 * 60 * 24 gives you number of millisecond in a day.

3. explicit cast to (int) gives you exact number of days.

Nothing more than this.