Java – Why is this Java code 6x faster than the identical C# code

c++execution-timejava

I have a few different solutions to Project Euler problem 5, but the execution time difference between the two languages/platforms in this particular implementation intrigues me. I didn't do any optimization with compiler flags, just plain javac (via commandline) and csc (via Visual Studio).

Here's the Java code. It finishes in 55ms.

public class Problem005b
{
    public static void main(String[] args)
    {
        long begin = System.currentTimeMillis();
        int i = 20;
        while (true)
        {
            if (
                    (i % 19 == 0) &&
                    (i % 18 == 0) &&
                    (i % 17 == 0) &&
                    (i % 16 == 0) &&
                    (i % 15 == 0) &&
                    (i % 14 == 0) &&
                    (i % 13 == 0) &&
                    (i % 12 == 0) &&
                    (i % 11 == 0)
                )
            {
                break;
            }
            i += 20;
        }
        long end = System.currentTimeMillis();
        System.out.println(i);
        System.out.println(end-begin + "ms");
    }   
}

Here is the identical C# code. It finishes in 320ms

using System;

namespace ProjectEuler05
{
    class Problem005
    {
        static void Main(String[] args)
        {
            DateTime begin = DateTime.Now;
            int i = 20;
            while (true)
            {
                if (
                        (i % 19 == 0) &&
                        (i % 18 == 0) &&
                        (i % 17 == 0) &&
                        (i % 16 == 0) &&
                        (i % 15 == 0) &&
                        (i % 14 == 0) &&
                        (i % 13 == 0) &&
                        (i % 12 == 0) &&
                        (i % 11 == 0)
                    )
                    {
                        break;
                    }
                i += 20;
            }
            DateTime end = DateTime.Now;
            TimeSpan elapsed = end - begin;
            Console.WriteLine(i);
            Console.WriteLine(elapsed.TotalMilliseconds + "ms");
        }
    }
}

Best Solution

  1. To time code execution, you should use the StopWatch class.
  2. Also, you have to account for the JIT, the runtime etc, so let the test run a sufficient amount of times (like 10,000, 100,000 times) and get some sort of average. It is important to run the code multiple times, not the program. So write a method, and loop in the main method to get your measurements.
  3. remove all debugging stuff from the assemblies and let the code run stand-alone in a release build