[java] How to convert nanoseconds to seconds using the TimeUnit enum?

How to convert a value from nanoseconds to seconds?

Here's the code segment:

import java.io.*;
import java.util.concurrent.*; 
..

class Stamper { 

public static void main (String[] args) { 
long start = System.nanoTime(); 
//some try with nested loops 
long end = System.nanoTime(); 
long elapsedTime = end - start;

System.out.println("elapsed: " + elapsedTime + "nano seconds\n");

//convert to seconds 
TimeUnit seconds = new TimeUnit(); 
System.out.println("which is " + seconds.toSeconds(elapsedTime) + " seconds"); 
}}

The error is

Stamper.java:16:  enum types may not be instantiated.

What does this mean?

TimeUnit is an enum, so you can't create a new one.

The following will convert 1000000000000ns to seconds.

TimeUnit.NANOSECONDS.toSeconds(1000000000000L);

You should write :

    long startTime = System.nanoTime();        
    long estimatedTime = System.nanoTime() - startTime;

Assigning the endTime in a variable might cause a few nanoseconds. In this approach you will get the exact elapsed time.

And then:

TimeUnit.SECONDS.convert(estimatedTime, TimeUnit.NANOSECONDS)

In Java 8 or Kotlin, I use Duration.ofNanos(1_000_000_000) like

val duration = Duration.ofNanos(1_000_000_000)
logger.info(String.format("%d %02dm %02ds %03d",
                elapse, duration.toMinutes(), duration.toSeconds(), duration.toMillis()))

Read more https://docs.oracle.com/javase/8/docs/api/java/time/Duration.html

This will convert a time to seconds in a double format, which is more precise than an integer value:

double elapsedTimeInSeconds = TimeUnit.MILLISECONDS.convert(elapsedTime, TimeUnit.NANOSECONDS) / 1000.0;

TimeUnit Enum

The following expression uses the TimeUnit enum (Java 5 and later) to convert from nanoseconds to seconds:

TimeUnit.SECONDS.convert(elapsedTime, TimeUnit.NANOSECONDS)

JDK9+ solution using java.time.Duration

Duration.ofNanos(1_000_000L).toSeconds()

https://docs.oracle.com/javase/9/docs/api/java/time/Duration.html#ofNanos-long-

https://docs.oracle.com/javase/9/docs/api/java/time/Duration.html#toSeconds--

To reduce verbosity, you can use a static import:

import static java.util.concurrent.TimeUnit.NANOSECONDS;

-and henceforth just type

NANOSECONDS.toSeconds(elapsedTime);