TimeUnit conversion from Milliseconds to Days not working for me

Question

I'm trying to get the difference of two timestamps in days, and TimeUnit is returning completely incorrect results for me.

Here is my code:

long ts = 1522242239952L;
long now = 1527274162820L;
long difference = now - ts;
int ageInDays = (int) TimeUnit.MILLISECONDS.convert(difference, TimeUnit.DAYS);
int ageInDays2 = (int) (difference/(1000 * 60 * 60 * 24));
System.out.println(ageInDays);
System.out.println(ageInDays2);

Output is:

-1756844032
58

Why is the TimeUnit calculation so incorrect ?

Answer 1

Because you're using TimeUnit.convert backwards. Try

TimeUnit.DAYS.convert(difference, TimeUnit.MILLISECONDS);

or just

TimeUnit.MILLISECONDS.toDays(difference);

Ref: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/TimeUnit.html#convert(long,%20java.util.concurrent.TimeUnit)