Julian date to regular date conversion

Question

How do i convert a julian date 2456606 which stands for Nov 18 2013 to the string format 18/11/2013 using java APIs? I tried executing the below code but it is not giving me the right answer. Any corrections to the below code are welcome

    String j = "2456606";
    Date date = new SimpleDateFormat("yyyyD").parse(j);
    String g = new SimpleDateFormat("dd.MM.yyyy").format(date);
    System.out.println(g);

Answer 1

tl;dr

LocalDate.MIN.with ( 
    java.time.temporal.JulianFields.MODIFIED_JULIAN_DAY , 
    2_456_606L 
)

2013-11-09

Other direction, from modern date to Julian Day.

 LocalDate.of( 2013 , 11 , 9 )
          .getLong ( java.time.temporal.JulianFields.JULIAN_DAY )

2456606

Details

Firstly, your comment:

the julian date to be 2456606 for nov 18 in the converter link mentioned below aa.usno.navy.mil/data/docs/JulianDate.php

…is incorrect. That web site returns November 9, 2013 for 2456606.

Your Navy web site defines Julian Date as a count of days since January 1, 4713 BC mapped to “Universal Time”. I assume they mean UTC and the modern ISO 8601 calendar system. See Wikipedia.

The java.time classes built into Java make this easy.

long input = 2_456_606L;
LocalDate ld = LocalDate.MIN.with ( java.time.temporal.JulianFields.JULIAN_DAY , input );

Dump to console.

System.out.println ( "input: " + input + " is: " + ld );

input: 2456606 is: 2013-11-09

For more discussion, see my Answer on a duplicate Question.

Going the other direction, converting a modern date to a Julian Day.

long output = ld.getLong ( java.time.temporal.JulianFields.JULIAN_DAY );

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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.

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

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

Where to obtain the java.time classes?

• Java SE 8 and SE 9 and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • 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.