Integer-To-Words-Java/NumberInWords.java at master · busaeed/Integer-To-Words-Java · GitHub

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public class NumberInWords {

    private static String[] singleDigit = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"};

    private static String[] tensDigits = {"", "ten", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"};

    private static String[] elevenToNineteenDigits = {"", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"};

    public static String convertNumberToWords(int number) {

        if (number >= 0 && number <= 9) { //0,1,...9

            return convertSingleDigit(number);

        } else if (number >= 10 && number <= 90 && number % 10 == 0) { //10,20,...90

            return convertTensDigits(number);

        } else if (number >= 11 && number <= 19) { //11,12,...19

            return convert11To19Digits(number);

        } else if (number >= 21 && number <= 99) { //21,22,...99

            return convertRestTwoDigits(number);

        } else if (number >= 100 && number <= 999) { //100,101,...999

            return convertHundreds(number);

        } else if (number >= 1000 && number <= 999999) { //1000,...999999

            return convertThousands(number);

        } else if (number >= 1000000 && number <= 999999999) { //1000000,...999999999

            return convertMilions(number);

        } else if (number >= 1000000000 && number <= 2147483647) { //1000000000,...2147483647

            return convertBilions(number);

        } else if (number <= -1 && number >= -2147483648) { //minus -1,...-2147483648

            return "minus " + convertNumberToWords(Math.abs(number));

        } else {

            throw new IllegalArgumentException("NOT AN INTEGER");

        }

    }

    private static String convertSingleDigit(int number) {

        return singleDigit[number];

    }

    private static String convertTensDigits(int number) {

        return tensDigits[number / 10];

    }

    private static String convert11To19Digits(int number) {

        return elevenToNineteenDigits[number - 10];

    }

    private static String convertRestTwoDigits(int number) {

        return tensDigits[number / 10] + " " + singleDigit[number % 10];

    }

    private static String convertHundreds(int number) {

        String hundredResult = singleDigit[number / 100] + " hundred";

        int remaining = number % 100;

        if (remaining != 0) {

            hundredResult += " " + convertNumberToWords(remaining);

        }

        return hundredResult;

    }

    private static String convertThousands(int number) {

        int thousand = number / 1000;

        String thousandResult = "";

        thousandResult = convertNumberToWords(thousand) + " thousand";

        int remaining = number % 1000;

        if (remaining != 0) {

            thousandResult += " and " + convertNumberToWords(remaining);

        }

        return thousandResult;

    }

    private static String convertMilions(int number) {

        int million = number / 1000000;

        String millionResult = "";

        millionResult = convertNumberToWords(million) + " million";

        int remaining = number % 1000000;

        if (remaining != 0) {

            millionResult += " and " + convertNumberToWords(remaining);

        }

        return millionResult;

    }

    private static String convertBilions(int number) {

        int billion = number / 1000000000;

        String billionResult = "";

        billionResult = convertNumberToWords(billion) + " billion";

        int remaining = number % 1000000000;

        if (remaining != 0) {

            billionResult += " and " + convertNumberToWords(remaining);

        }

        return billionResult;

    }

}