How to measure the a time-span in seconds using System.currentTimeMillis()?

Question

How to convert System.currentTimeMillis(); to seconds?

long start6=System.currentTimeMillis();
System.out.println(counter.countPrimes(100000000)         


        

Answer 1

Java 8 now provides the most concise method to get current Unix Timestamp:

Instant.now().getEpochSecond();