Why does the new Java 8 Date Time API not have nanosecond precision? [duplicate]

Question

One of the features of the new Date Time API in Java 8 is supposed to be nanosecond precision. However when I print the current Date Time to the console like so

DateTimeFormatter formatter = DateTimeFormatter     .ofPattern("yyyy-MM-dd'T'HH:mm:ss,nnnnnnnnnZ"); System.out.println(OffsetDateTime.now().format(formatter));  

I only see millisecond precision: 2015-11-02T12:33:26,746000000+0100

The operating system does seem to support nanosecond precision. When I print the current date time via the Terminal

date -Ins 

I see 2015-11-02T12:33:26,746134417+0100

How do I get nanosecond precision in Java? I'm running Oracle Java 1.8.0_66 on Ubuntu 14.04 64-bit

Answer 1

The java.time API in general does have nanosecond precision. For example:

DateTimeFormatter formatter = DateTimeFormatter     .ofPattern("yyyy-MM-dd'T'HH:mm:ss,nnnnnnnnnZ"); OffsetDateTime odt = OffsetDateTime.of(2015, 11, 2, 12, 38, 0, 123456789, ZoneOffset.UTC); System.out.println(odt.format(formatter)); 

Output:

2015-11-02T12:38:00,123456789+0000 

However, it's the clock value returned by OffsetDateTime.now() which is returning a value which only has milliseconds.

From Clock implementation in Java 8:

The clock implementation provided here is based on System.currentTimeMillis(). That method provides little to no guarantee about the accuracy of the clock. Applications requiring a more accurate clock must implement this abstract class themselves using a different external clock, such as an NTP server.

So there's nothing inherently imprecise here - just the default implementation of Clock using System.currentTimeMillis(). You could potentially create your own more precise subclass. However, you should note that adding more precision without adding more accuracy probably isn't terribly useful. (There are times when it might be, admittedly...)