How to calculate nanoseconds from 1800-CodePudding

I'm trying to calculate the number of nano seconds that passed from: 11-Nov-1831 00:00:00.00

to a given date.

I tried to use alot of packages but none of them succed in the mission (the closest was Instant)

What's the best way to achive this mission?

CodePudding user response：

Instant is still the best option, but you may need some helper objects.

For instance, to create the start date (replace the Z with a different time zone or offset as needed):

Instant start = Instant.parse("1831-11-11T00:00:00Z");

Then take the given date. You can parse it, or use conversion methods. For instance, if you have a LocalDateTime (use a different ZoneId or ZoneOffset as needed):

LocalDateTime localDateTime = LocalDateTime.parse("2022-06-09T20:56");
Instant instant = localDateTime.atZone(ZoneId.systemDefault()).toInstant();

Now get a duration:

Duration duration = Duration.between(start, instant);
long nanos = duration.toNanos();

CodePudding user response：

import java.text.SimpleDateFormat;
import java.util.Date;

public class Main {
    public static void main(String[] args) throws Exception {
        long nowInMilliSeconds = System.currentTimeMillis();
        
        Date baseDate = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss").parse("11-Nov-1831 00:00:00.00");
        long baseDateInMilliSeconds = baseDate.getTime();
        
        long nanoSecondsSinceBaseDate = (nowInMilliSeconds - baseDateInMilliSeconds)* 1000000;
        //The (nowInMilliSeconds - baseDateInMilliSeconds) is in milli seconds thus multiplied by 1000000 that gives difference in nano seconds
        System.out.println(nanoSecondsSinceBaseDate);
    }
}

Each day in nano seconds: 24*3600*1000000000

Each year in nano seconds: 365*24*3600*1000000000

Compute approximate expected result using these formulas and compare with method's result to check the output