Java - AYUDA! PROGRAMA PARA LEER NUMERO Y IMPRIMIRLO EN LETRAS

package app;

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        String unidades[] = {"cero", "uno", "dos" ,"tres" ,"cuatro" ,"cinco" ,

                "seis" ,"siete" ,"ocho" ,"nueve","diez"};

        String especiales[] = {"once", "doce","trece","catorce", "quince",

                "diezciseis", "diecisiete", "dieciocho", "diecinueve",};

        String decenas[] = {"veinte", "treinta","cuarenta","cincuenta", "sesenta",

                "setenta", "ochenta", "noventa"};

        String centena [] = {"cien", "doscientos", "trecientos", "cuatrocientos",

                "quinientos", "seicientos", "setecientos", "Ochocientos", "novecientos"};

        String millares [] = {"mil", "dosmil", "tresmil", "cuatromil", "cincomil",

                "seismil", "sietemil", "ochomil", "nuevemil"};

        Scanner scanner = new Scanner(System.in);

        System.out.print("Ingrese un numero entre 0-9999:");

        int num = scanner.nextInt();

        if(num>=0 && num<11)

            System.out.print('\n' + unidades[num]);

        else if(num<20)

            System.out.print('\n' + especiales[num]);

        else if(num<1000)

            System.out.print('\n' + centena[num]);

        else if (num<10000){

            int unid = num % 1000;

            int dec = num/1000;

            int cen = num%1000;

            int mill = num/1000;

            if(unid == 0)

                System.out.print(millares[mill] + " " + centena[cen] + " " + decenas[dec] + " " + unidades[unid]);

            else

                System.out.print(millares[mill] + " " + centena[cen] + " " + decenas[dec] + " y " + unidades[unid]);

        }

        else

            System.out.print("El numero debe ser menor a 9999");

    }

}

/**

 *

 * @author andreas

 */

public class NumberToLetters {

    private final int MAX_VALUE = 9999;

    private int[] digitos;

    private final String[][] letters = {

        {"uno", "dos", "tres", "cuatro", "cinco", "seis", "siete", "ocho", "nueve"},

        {"diez", "veinte", "treinta", "cuarenta", "cincuenta", "sesenta", "setenta", "ochenta", "noventa"},

        {"ciento", "doscientos", "trescientos", "cuatrocientos", "quinientos", "seicientos", "setecientos", "ochocientos", "novecientos"},

        {"mil", "dos mil", "tres mil", "cuatro mil", "cinco mil", "seis mil", "siete mil", "ocho mil", "nueve mil"}

    };

    private final String[][] especial = {

        {

            "diez",

            "once",

            "doce",

            "trece",

            "catorce",

            "quince",

            "dieciséis",

            "diecisiete",

            "dieciocho",

            "diecinueve"

        },

        {

            "veinte",

            "veintiuno",

            "veintidós",

            "veintitrés",

            "veinticuatro",

            "veinticinco",

            "veintiséis",

            "veintisiete",

            "veintiocho",

            "veintinueve"

        }

    };

    private void inicializaDigitos(int numero) {

        String numeroToString = Integer.toString(numero);

        digitos = new int[numeroToString.length()];

        int j = 0;

        for (int i = numeroToString.length() - 1; i > 0; i--) {

            digitos[j++] = Integer.parseInt(numeroToString.substring(i, i + 1));

        }

        digitos[j] = Integer.parseInt(numeroToString.substring(0, 1));

    }

    private String procesarDecenas() {

        if (1 == digitos.length) {

            return letters[0][digitos[0] - 1];

        } else if (digitos.length >= 2) {

            if ((1 == digitos[1] || 2 == digitos[1])) {

                return especial[digitos[1] - 1][digitos[0]];

            } else {

                StringBuilder sb = new StringBuilder();

                for (int i = 1; i >= 0; i--) {

                    if (0 == digitos[i]) {

                        continue;

                    }

                    sb.append(letters[i][digitos[i] - 1]);

                    sb.append(" y ");

                }

                return sb.substring(0, sb.length() - 2).toString();

            }

        }

        return null;

    }

    private String procesarHastaDecenas() {

        StringBuilder sb = new StringBuilder();

        for (int i = digitos.length - 1; i >= 2; i--) {

            if (0 == digitos[i]) {

                continue;

            }

            sb.append(letters[i][digitos[i] - 1]);

            sb.append(" ");

        }

        return sb.toString();

    }

    public String obtenerLetras() {

        StringBuilder sb = new StringBuilder();

        sb.append(procesarHastaDecenas());

        sb.append(procesarDecenas());

        return sb.toString();

    }

    public NumberToLetters(int numero) {

        if (0 > numero || MAX_VALUE < numero) {

            throw new IllegalArgumentException("Verifique el numero");

        }

        inicializaDigitos(numero);

    }

    public static void main(String[] args) {

        NumberToLetters ntl = new NumberToLetters(726);

        System.out.println(ntl.obtenerLetras());

    }

}

Exception in thread "main" java.lang.ClassNotFoundException: app.Main

	at java.net.URLClassLoader.findClass(URLClassLoader.java:381)

	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)

	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)

	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)

	at java.lang.Class.forName0(Native Method)

	at java.lang.Class.forName(Class.java:264)

	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:123)

public static void main(String[] args) {

        Scanner scanner = null;

        try {

            System.out.print("Ingresa numero: ");

            scanner = new Scanner(System.in);

            int numero = scanner.nextInt();

            NumberToLetters ntl = new NumberToLetters(numero);

            System.out.println(ntl.obtenerLetras());

        } catch (Exception e) {

        } finally {

            if (null != scanner) {

                scanner.close();

            }

        }

    }