I need to write a program where the program would generate random letter and i would need to store this random character into an array

        char[] arrayRandom = new char[10];


        for (int i = 0; i < 8; i++) {
            randomNumLet = (generator.nextInt(20) + 1);
            System.out.print(arrayRandomLetter[randomNumLet] + " ");
            arrayRandomLetter[randomNumLet] = arrayRandom[i];
        }

is there anything wrong with my code? because when i run this and printed the array i get boxes for all the values in the array and there are some letter that this line of code cannot print

            System.out.print(arrayRandomLetter[randomNumLet] + " ");

Thanks