Example: Convert Digit Number to Words in Java

// Convert Digit Number to Words
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {

    private static final String[] units = {
        "", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten",
        "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen",
        "Eighteen", "Nineteen"
    };

    private static final String[] tens = {
        "", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"
    };

    private static final String[] scales = {
        "", "Thousand", "Million", "Billion", "Trillion"
    };

    public static String convertToWords(long number) {
        if (number == 0) {
            return "Zero";
        }

        String words = "";
        int scaleIndex = 0;

        while (number > 0) {
            if (number % 1000 != 0) {
                words = convertLessThanOneThousand((int) (number % 1000)) + " " + scales[scaleIndex] + " " + words;
            }
            number /= 1000;
            scaleIndex++;
        }
        return words.trim();
    }

    private static String convertLessThanOneThousand(int number) {
        String current;

        if (number % 100 < 20) {
            current = units[number % 100];
            number /= 100;
        } else {
            current = units[number % 10];
            number /= 10;
            current = tens[number % 10] + " " + current;
            number /= 10;
        }
        if (number > 0) {
            current = units[number] + " Hundred " + current;
        }
        return current.trim();
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        long number = scanner.nextLong();
        scanner.close();

        System.out.println("Word representation: " + convertToWords(number));
    }
}