Java Cookbook

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 ...