Convert Integers Dollar Amounts to English Words

 /**  
  * Solution is in java  
  * <p>  
  * "C:\Program Files\Java\jdk1.8.0_192\bin\java.exe"  
  * Input : 987654  
  * NineHundredEightySevenThousandSixHundredFiftyFourDollars  
  * Input : 111111111  
  * OneHundredElevenMillionOneHundredElevenThousandOneHundredElevenDollars  
  * Input : 911  
  * NineHundredElevenDollars  
  * <p>  
  * Process finished with exit code 0  
  */  
 import java.util.*;  
 import java.util.concurrent.ThreadLocalRandom;  
 public class DollarsToEnglishConverter {  
   private static final Map<Integer, String> DIGIT_TO_STRING = new HashMap<>();  
   static {  
     DIGIT_TO_STRING.put(1, "One");  
     DIGIT_TO_STRING.put(2, "Two");  
     DIGIT_TO_STRING.put(3, "Three");  
     DIGIT_TO_STRING.put(4, "Four");  
     DIGIT_TO_STRING.put(5, "Five");  
     DIGIT_TO_STRING.put(6, "Six");  
     DIGIT_TO_STRING.put(7, "Seven");  
     DIGIT_TO_STRING.put(8, "Eight");  
     DIGIT_TO_STRING.put(9, "Nine");  
     DIGIT_TO_STRING.put(10, "Ten");  
     DIGIT_TO_STRING.put(11, "Eleven");  
     DIGIT_TO_STRING.put(12, "Twelve");  
     DIGIT_TO_STRING.put(13, "Thirteen");  
     DIGIT_TO_STRING.put(14, "Fourteen");  
     DIGIT_TO_STRING.put(15, "Fifteen");  
     DIGIT_TO_STRING.put(16, "Sixteen");  
     DIGIT_TO_STRING.put(17, "Seventeen");  
     DIGIT_TO_STRING.put(18, "Eighteen");  
     DIGIT_TO_STRING.put(19, "Nineteen");  
     DIGIT_TO_STRING.put(20, "Twenty");  
     DIGIT_TO_STRING.put(30, "Thirty");  
     DIGIT_TO_STRING.put(40, "Forty");  
     DIGIT_TO_STRING.put(50, "Fifty");  
     DIGIT_TO_STRING.put(60, "Sixty");  
     DIGIT_TO_STRING.put(70, "Seventy");  
     DIGIT_TO_STRING.put(80, "Eighty");  
     DIGIT_TO_STRING.put(90, "Ninety");  
     DIGIT_TO_STRING.put(100, "Hundred");  
     DIGIT_TO_STRING.put(1000, "Thousand");  
     DIGIT_TO_STRING.put(10000, "TenThousand");  
     DIGIT_TO_STRING.put(100000, "HundredThousand");  
     DIGIT_TO_STRING.put(1000000, "Million");  
     DIGIT_TO_STRING.put(10000000, "TenMillion");  
     DIGIT_TO_STRING.put(100000000, "HundredMillion");  
     DIGIT_TO_STRING.put(1000000000, "Billion");  
   }  
   public static void main(String[] args) {  
     DollarsToEnglishConverter converter = new DollarsToEnglishConverter();  
     List<Integer> candidates = converter.validateInputAndGetValue();  
     candidates.forEach(candidate -> {  
       System.out.format("Input : %d%n", candidate);  
       List<Integer> digits = converter.convertNumberToComponentDigitsInReverse(candidate);  
       List<String> text = converter.convertToEnglish(digits);  
       text.forEach(System.out::print);  
       System.out.println("Dollars");  
     });  
   }  
   private List<String> convertToEnglish(List<Integer> digits) {  
     List<String> text = new ArrayList<>();  
     List<Integer> subList = new ArrayList<>();  
     for (int counter = 0; digits.size() > 0; counter++) {  
       do {  
         subList.add(digits.remove(0));  
         if (subList.size() == 3) break;  
       } while (!digits.isEmpty());  
       if (counter > 0) {  
         int power = (int) Math.pow(1000, counter);  
         text.add(0, DIGIT_TO_STRING.get(power));  
       }  
       text.addAll(0, computeInHundreds(subList));  
       subList.clear();  
     }  
     if (text.isEmpty()) {  
       text.add("Zero");  
     }  
     return text;  
   }  
   private List<String> computeInHundreds(List<Integer> digits) {  
     if (digits.size() > 3) {  
       throw new RuntimeException("digits should be sent only in hundreds!");  
     }  
     List<String> text = new ArrayList<>();  
     for (int i = 0; i < digits.size(); i++) {  
       int power = (int) Math.pow(10, i);  
       int digit = power * digits.get(i);  
       if (digit == 0) {  
         continue;  
       }  
       if (i == 1 && digits.get(i) == 1) {  
         if (digits.get(i - 1) != 0) {  
           text.remove(i - 1);  
         }  
         digit = 10 + digits.get(i - 1);  
       }  
       if (i == 2) {  
         text.add(0, DIGIT_TO_STRING.get(power));  
         text.add(0, DIGIT_TO_STRING.get(digits.get(i)));  
       } else {  
         text.add(0, DIGIT_TO_STRING.get(digit));  
       }  
     }  
     return text;  
   }  
   private List<Integer> convertNumberToComponentDigitsInReverse(int candidate) {  
     if (candidate < 0) {  
       throw new RuntimeException("Value cannot be Negative!");  
     }  
     List<Integer> digits = new LinkedList<>();  
     while (candidate > 0) {  
       digits.add(candidate % 10);  
       candidate = candidate / 10;  
     }  
     return digits;  
   }  
   private List<Integer> validateInputAndGetValue() {  
     List<Integer> data = new ArrayList<>();  
     try {  
       data.add(1);  
       data.add(717);  
       data.add(1111);  
       data.add(1000);  
       data.add(0);  
       for (int i = 0; i < 100; i++) {  
         data.add(ThreadLocalRandom.current().nextInt(1, 199999999));  
       }  
     } catch (final Exception e) {  
       throw new RuntimeException("Not a valid String ", e);  
     }  
     return data;  
   }  
 }