Error using Random in JAVA

Question

When I run this code:

public class main 
{
    static boolean terminar = false;

    public static void main(String[] args)
    {
        long init  = System.currentTimeMillis(); 

        BruteForce(true, true, "a123", 10, 10000);

        long end  = System.currentTimeMillis(); 
        long diff = end - init;
        System.out.println("Demorou " + (diff / 1000) + " segundos");
    }
    public static String BruteForce(boolean numeros, boolean letras, String busca,int maxCaracteres,  int limite)
    {
        ArrayList<String> old = new ArrayList<String>();
        ArrayList<String> caracteres = new ArrayList<String>();

        Random rand = new Random();

        String[] todos = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "a", "b", "c", "d", "e", "f", "g"
                          , "h", "i", "j", "k", "l", "m", "n", "o", "p", "k", "r", "s", "t", "u", "v", "w", "x", "y", "z"
                          , "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U"
                          , "V", "W", "X", "Y", "Z", "'", "!", "@", "#", "$", "£", "%", "¢", "¨", "¬", "&", "*", "(", ")", "_", "-"
                          , "+", "=", "§", "/", ".", "[", "]", "`", "´", "{", "}", "º", "^", "~", "<", ">", ":", ";", "?", "°", "ª",
                          "|", "¹", "²", "³"};

        for(int j = 0; j < todos.length; j++)
        {
            caracteres.add(todos[j]);
        }

        String combinacao = "";
        int quantCaracteres = 1;
        int stop = todos.length * quantCaracteres;

        while(old.size() != stop)
        {   
            for(int i = 0; i < quantCaracteres; i++)
            {
                int randomico = rand.nextInt(todos.length + 1);

                combinacao = "" + combinacao + todos[randomico];
            }

            if(combinacao.equals(busca))
            {
                return combinacao;
            }

            if(!old.contains(combinacao))
            {
                old.add(combinacao);
                System.out.println("Size:" + old.size() + " Stop:" + (stop -1) + " Todos:" + todos.length);
                System.out.println(combinacao);
            }

            combinacao = "";

            if(old.size() == stop)
            {
                quantCaracteres++;
            }
        }

        return "Nada";
    }
}

He makes that mistake

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 107
at me.lordlokon.main.BruteForce(main.java:49)
at me.lordlokon.main.main(main.java:14)

The line 49 is this:

combinacao = "" + combinacao + todos[randomico];

Answer 1

Look at this:

        int randomico = rand.nextInt(todos.length + 1);

        combinacao = "" + combinacao + todos[randomico];

According to the javadocs of the method nextInt(int):

Returns a pseudorandom, uniformly Distributed int value between 0 (inclusive) and the specified value (exclusive)

What translating into Portuguese is:

Returns a pseudorandom, evenly distributed int value between 0 (inclusive) and the specified value (exclusive)

That is, it will be between 0 and todos.length.

Aconntece that the last array position todos is the position todos.length - 1. When the generated number is todos.length, will give a ArrayIndexOutOfBoundsException.

What you wanted was this:

        int randomico = rand.nextInt(todos.length);

        combinacao = "" + combinacao + todos[randomico];

I mean, just take the + 1 of the code.

And finally, a hint that has nothing to do with random numbers: Follow the language naming conventions. The class name main should start with uppercase letter and method name BruteForce should start with lower case letter.