Formatting number on Android - issue

What I'm trying to accomplish is to get the code to format the number according to these rules:

If number is integer smaller than 10^6 or bigger than 10^-6, write it as integer, else write it in scientific format, rounded to 8 decimal places at most.

If number is decimal smaller than 10^6 or bigger than 10^-6, write it as decimal with 8 decimal places at most, else write it in scientific format, rounded to 8 places at most.

I got this code, but it doesn't work as it should:

BigDecimal upperLimit = BigDecimal.valueOf(1000000);
    BigDecimal lowerLimit = BigDecimal.valueOf(0.000001);
    BigDecimal bigNum = BigDecimal.valueOf(result);
    String string = bigNum.toString();
    if (bigNum.scale() <= 0) {
        if (bigNum.compareTo(upperLimit) < 0 && bigNum.compareTo(lowerLimit) > 0) {
            BigInteger integer = bigNum.toBigInteger();
            string = integer.toString();
        }
        else {
            int index = string.indexOf('0');
            if (index < 8) {
                string = format(bigNum, index - 2);
            }
            else {
                string = format(bigNum, 8);
            }
        }
    }
    else {
        if (bigNum.compareTo(upperLimit) < 0 && bigNum.compareTo(lowerLimit) > 0) {
            string = bigNum.toString();
            int index = string.indexOf('.');
            string = string.substring(index, 8);
        }
        else {
            string = format(bigNum, 8);
        }
    }

private static String format (BigDecimal x, int scale) {
    NumberFormat formatter = new DecimalFormat("0.0E0");
    formatter.setRoundingMode(RoundingMode.HALF_UP);
    formatter.setMinimumFractionDigits(scale);
    return formatter.format(x);
}

here is what it outputs:

input 123*2 (246) -> output 246 ✓

input 123.2*2 (246.4) -> crash

input 132.2*100000000 -> output 1.32200000e10 ✓

input 13222*10000 -> output 1.3e8 (should be 1.3222e8)

So as you can see, small integers are formatted well, but other types aren't. How to fix this and where is the problem, because I can't seem to find any?

Thank you for helping with this code.

NOTE: anyone can use this code for anything he needs once it's fixed.