Question

I’m trying to time the performance of my program by using System.currentTimeMillis() (or alternatively System.nanoTime()) and I’ve noticed that every time I run it – it gives a different result for time it took to finish the task.

Even the straightforward test:

long totalTime;
long startTime;
long endTime;
startTime = System.currentTimeMillis();
for (int i = 0; i < 1000000000; i++)
{
    for (int j = 0; j < 1000000000; j++)
    {
    }
}
endTime = System.currentTimeMillis();
totalTime = endTime-startTime;
System.out.println("Time: " + totalTime);

produces all sorts of different outputs, from 0 to 200. Can anyone say what I’m doing wrong or suggest an alternative solution?

Answer 1

The loop doesn’t do anything, so you are timing how long it takes to detect the loop is pointless.

Timing the loops more accurately won’t help, you need to do something slightly useful to get repeatable results.

I suggest you try -server if you are running on 32-bit windows.

A billion billion clock cycles takes about 10 years so its not really iterating that many times.