Recipe 6.6 Converting Epoch Seconds to DMYHMS

Problem

You need to convert a number of seconds since 1970 into a Date.

Solution

Just use the Date constructor.

Discussion

"The Epoch" is the beginning of time as far as modern operating systems go. Unix time, and some versions of Windows time, count off inexorably the seconds since the epoch. On systems that store this in a 32-bit integer, time is indeed running out. Let's say we wanted to find out when the Unix operating system, whose 32-bit versions use a 32-bit date, will get into difficulty. We take a 32-bit integer of all ones, and construct a Date around it. The Date constructor needs the number of milliseconds since 1970, so we multiply by 1,000:

/** When does the UNIX date get into trouble? */ public class Y2038 {     public static void main(String[] a) {         // This should yield 2038AD, the hour of doom for the         // last remaining 32-bit UNIX systems (there will be         // millions of 64-bit UNIXes by then).         long expiry = 0x7FFFFFFFL;         System.out.println("32-bit UNIX expires on " +             Long.toHexString(expiry) + " or " +             new java.util.Date(expiry  * 1000));     } }

Sure enough, the program reports that 32-bit Unixes will expire in the year 2038 (you might think I knew that in advance if you were to judge by the name I gave the class; in fact, my web site has carried the Y2038 warning to Unix users for several years now). At least Unix system managers have more warning than most of the general public had for the original Y2K problem.

> java Y2038 32-bit UNIX expires on 7fffffff or Mon Jan 18 22:14:07 EST 2038 >

At any rate, if you need to convert seconds since 1970 to a date, you know how.