Ratio

private void calculatePi()
{
    Random rand = new Random();

    int alreadyReduced = 0;
    // reuse totalLoops instead of magic numbers throughout the code
    final int totalLoops = 5000;
    for (int i = 0; i < totalLoops; ++i)
    {
        // ensure the randomly generated number is greater than 0
        int numerator = Math.abs(rand.nextInt()) + 1;
        int denominator = Math.abs(rand.nextInt()) + 1;

        Ratio ratio = new Ratio(numerator, denominator);

        if (numerator == ratio.getNumerator() && denominator == ratio.getDenominator())
        {
            alreadyReduced++;
        }
    }

    double probability = ((double) alreadyReduced / (double) totalLoops);
    double pi = Math.sqrt(6.0 / probability);

    /*
     *  html tags are used to force word wrapping
     *  use String.format to limit the representation of pi to 3 decimal places
     */
    myLabel.setText(String.format("<html>\u03C0 is approximately %.3f</html>", pi));
}