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

long start = System.currentTimeMillis();
counter.countPrimes(1000000);
long end = System.currentTimeMillis();

System.out.println("Took : " + ((end - start) / 1000));

UPDATE

An even more accurate solution would be:

final long start = System.nanoTime();
counter.countPrimes(1000000);
final long end = System.nanoTime();

System.out.println("Took: " + ((end - start) / 1000000) + "ms");
System.out.println("Took: " + (end - start)/ 1000000000 + " seconds");