Java calculate elapsed time

package com.w3schools;
 
import java.util.concurrent.TimeUnit;
 
public class ElapsedTimeTest {
  public static void main(String args[]) throws InterruptedException{
	  //start
	  long lStartTime = System.nanoTime();
	  //task
	  calculation();
	  //end
	  long lEndTime = System.nanoTime();
	  //time elapsed
	  long output = lEndTime - lStartTime;
	  System.out.println("Elapsed time in milliseconds: " + output / 1000000);
  }
 
  private static void calculation() throws InterruptedException {
      //Sleep 3 seconds
      TimeUnit.SECONDS.sleep(3);
  }
}

Elapsed time in milliseconds: 3002