Comparing Dates
Problem
You need to compare two dates.
Solution
If the dates are in Date
objects,
compare
with equals( )
and one of before( )
or after( )
. If the dates are in
longs
, compare with both
==
and one of
<
or >
.
Discussion
While Date
implements equals( )
like any good class, it also provides before(Date)
and after(Date)
, which compare one date with
another to see which happened first. This can be used to determine
the relationship among any two dates, as in Example 6-1.
Example 6-1. CompareDates.java
import java.util.*; import java.text.*; public class CompareDates { public static void main(String[] args) throws ParseException { DateFormat df = new SimpleDateFormat ("yyyy-MM-dd"); // Get Date 1 Date d1 = df.parse(args[0]); // Get Date 2 Date d2 = df.parse(args[1]); String relation; if (d1.equals(d2)) relation = "the same date as"; else if (d1.before(d2)) relation = "before"; else relation = "after"; System.out.println(d1 + " is " + relation + ' ' + d2); } }
Running CompareDates
with two close-together dates
and the same date reveals that it seems to work:
> java CompareDates 2000-01-01 1999-12-31 Sat Jan 01 00:00:00 EST 2000 is after Fri Dec 31 00:00:00 EST 1999 > java CompareDates 2000-01-01 2000-01-01 Sat Jan 01 00:00:00 EST 2000 is the same date as Sat Jan 01 00:00:00 EST 2000
It would be interesting to see if
DateFormat.parse( )
really does field rolling, as the documentation says.
Apparently so!
> javaCompareDates 2001-02-29 2001-03-01 Thu Mar 01 00:00:00 EST 2001 ...
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