public static Double convertTextToNumber()

in poi/src/main/java/org/apache/poi/ss/formula/functions/Value.java [86:215]
112 lines of code
37 McCabe index (conditional complexity)

    public static Double convertTextToNumber(String strText) {
        boolean foundCurrency = false;
        boolean foundUnaryPlus = false;
        boolean foundUnaryMinus = false;
        boolean foundPercentage = false;

        int len = strText.length();
        int i;
        for (i = 0; i < len; i++) {
            char ch = strText.charAt(i);
            if (Character.isDigit(ch) || ch == '.') {
                break;
            }
            switch (ch) {
                case ' ':
                    // intervening spaces between '$', '-', '+' are OK
                    continue;
                case '$':
                    if (foundCurrency) {
                        // only one currency symbols is allowed
                        return null;
                    }
                    foundCurrency = true;
                    continue;
                case '+':
                    if (foundUnaryMinus || foundUnaryPlus) {
                        return null;
                    }
                    foundUnaryPlus = true;
                    continue;
                case '-':
                    if (foundUnaryMinus || foundUnaryPlus) {
                        return null;
                    }
                    foundUnaryMinus = true;
                    continue;
                default:
                    // all other characters are illegal
                    return null;
            }
        }
        if (i >= len) {
            // didn't find digits or '.'
            if (foundCurrency || foundUnaryMinus || foundUnaryPlus) {
                return null;
            }
            return ZERO;
        }

        // remove thousands separators

        boolean foundDecimalPoint = false;
        int lastThousandsSeparatorIndex = Short.MIN_VALUE;

        StringBuilder sb = new StringBuilder(len);
        for (; i < len; i++) {
            char ch = strText.charAt(i);
            if (Character.isDigit(ch)) {
                sb.append(ch);
                continue;
            }
            switch (ch) {
                case ' ':
                    String remainingTextTrimmed = strText.substring(i).trim();
                    // support for value[space]%
                    if (remainingTextTrimmed.equals("%")) {
                        foundPercentage = true;
                        break;
                    }
                    if (remainingTextTrimmed.length() > 0) {
                        // intervening spaces not allowed once the digits start
                        return null;
                    }
                    break;
                case '.':
                    if (foundDecimalPoint) {
                        return null;
                    }
                    if (i - lastThousandsSeparatorIndex < MIN_DISTANCE_BETWEEN_THOUSANDS_SEPARATOR) {
                        return null;
                    }
                    foundDecimalPoint = true;
                    sb.append('.');
                    continue;
                case ',':
                    if (foundDecimalPoint) {
                        // thousands separators not allowed after '.' or 'E'
                        return null;
                    }
                    int distanceBetweenThousandsSeparators = i - lastThousandsSeparatorIndex;
                    // as long as there are 3 or more digits between
                    if (distanceBetweenThousandsSeparators < MIN_DISTANCE_BETWEEN_THOUSANDS_SEPARATOR) {
                        return null;
                    }
                    lastThousandsSeparatorIndex = i;
                    // don't append ','
                    continue;

                case 'E':
                case 'e':
                    if (i - lastThousandsSeparatorIndex < MIN_DISTANCE_BETWEEN_THOUSANDS_SEPARATOR) {
                        return null;
                    }
                    // append rest of strText and skip to end of loop
                    sb.append(strText.substring(i));
                    i = len;
                    break;
                case '%':
                    foundPercentage = true;
                    break;
                default:
                    // all other characters are illegal
                    return null;
            }
        }
        if (!foundDecimalPoint) {
            if (i - lastThousandsSeparatorIndex < MIN_DISTANCE_BETWEEN_THOUSANDS_SEPARATOR) {
                return null;
            }
        }
        double d;
        try {
            d = Double.parseDouble(sb.toString());
        } catch (NumberFormatException e) {
            // still a problem parsing the number - probably out of range
            return null;
        }
        double result = foundUnaryMinus ? -d : d;
        return foundPercentage ? result / 100. : result;
    }