Java, set date to 0/0/0

Question

I have an object with some dates and I'd like to return them in the getter. The problem is that i need to do Date.toString(); because I have to print them, and when the date is null I get a NullPointerException.

I was thinking about returning the date 0/0/0 when the date is null, but I don't know how to set this value. Is there any way? Just like new Date(0) returns the 1970-01-01-00:00:00, is there anything similar to this but to return 0/0/0?

Thanks!

Answer 1

There is no Date 0/0/0, by definition, as there is no Day 0 and no Month 0. A day is a member of the set {1,..,28 or 30 or 31} and month is a member of the set {1,...12}. Hence, it is impossible - and it is good that it is impossible - to express 0/0/0 as Date Object.

Answer 2

The terrible Date and Calendar classes were supplanted years ago by the java.time classes.

LocalDate

The LocalDate class represents a date-only value without time-of-day and without time zone or offset-from-UTC.

You may set the month by a number, with sane numbering 1-12 for January-December.

LocalDate ld = LocalDate.of( 1986 , 2 , 23 ) ;  // Years use sane direct numbering (1986 means year 1986). Months use sane numbering, 1-12 for January-December.

Or, better, use the Month enum objects pre-defined, one for each month of the year. Tip: Use these Month objects throughout your codebase rather than a mere integer number to make your code more self-documenting, ensure valid values, and provide type-safety. Ditto for Year & YearMonth.

LocalDate ld = LocalDate.of( 1986 , Month.FEBRUARY , 23 ) ;

Zero-date senseless

is there anything similar to this but to return 0/0/0?

No.

Trying to represent a null with a date of all zeros is the wrong way to go. There is no such thing as a date of all zeros (year, month, and day all being zero).

Instead, pick an arbitrary date to use as a special value. Document thoroughly your choice and its meaning.

Do not choose a date too distant in time. Many libraries and databases are limited in their range of values. You do not want your data to break there.

Generally I would suggest using the epoch of 1970-01-01T00:00:00Z, the first moment of 1970 in UTC (the Z means UTC, and is pronounced “Zulu”). This moment is used as the epoch reference for Unix, the legacy date-time classes bundled with Java, and the modern date-time classes built into Java 8 and later. So many programmers and sysadmins will recognize this moment as special. The java.time classes include a constant for your convenience: Instant.EPOCH.

Obviously my suggestion applies to common business-oriented apps interested in forward-looking near dates, with past history not reaching back to 1970. If that does not meet your needs, pick another arbitrary value, such as 1900-01-01.

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, Java SE 11, and later - Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.