Question

I would like to compare the speed performance (if there were any) from the two readDataMethod() as I illustrate below.

private void readDataMethod1(List<Integer> numbers) {
    final long startTime = System.nanoTime();
    for (int i = 0; i < numbers.size(); i++) {
        numbers.get(i);
    }
    final long endTime = System.nanoTime();
    System.out.println("method 1 : " + (endTime - startTime));
}

private void readDataMethod2(List<Integer> numbers) {
    final long startTime = System.nanoTime();
    int i = numbers.size();
    while (i-- > 0) {
        numbers.get(i);
    }
    final long endTime = System.nanoTime();
    System.out.println("method 2 : " + (endTime - startTime));
}

Most of the time the result I get shows that method 2 has “lower” value.

   Run         readDataMethod1    readDataMethod2

     1                  636331             468876
     2                  638256             479269
     3                  637485             515455
     4                  716786             420756

Does this test prove that the readDataMethod2 is faster than the earlier one ?

Answer 1

Does this test prove that the readDataMethod2 is faster than the earlier one ?

You are on the right track in that you’re measuring comparative performance, rather than making assumptions.

However, there are lots of potential issues to be aware of when writing micro-benchmarks in Java. I would recommend that you read
How do I write a correct micro-benchmark in Java?