strip time from timestamp

Question

Why cannot I clear the time from a timestamp this way:

one day == 24 * 3600 * 1000 == 86400000 milliseconds.

long ms = new Date().getTime();  //Mon Sep 03 10:06         


        

Answer 1

I actually want to compare it to another date not taking into account time of day

To compare dates I suggest using JodaTime which supports this functionality with LocalDate

LocalDate date1 = new LocalDate(); // just the date without a time or time zone
LocalDate date2 = ....
if (date1.compareTo(date2) <=> 0)

Note: this will construct timezone-less LocalDates which is appropriate for the default timezone. As long as you are only talking about the timezone where the default timezone for the machine has been set, this is fine. e.g. say you have a timezone of CEST then this is fine for most of Europe.

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Using the built in time functions you can do something like

public static int compareDatesInTimeZone(Date d1, Date d2, TimeZone tz) {
    long t1 = d1.getTime();
    t1 += tz.getOffset(t1);
    long t2 = d2.getTime();
    t2 += tz.getOffset(t2);
    return Double.compare(t1 / 86400000, t2 / 86400000);
}