Inserting multiple random chars into database table JAVA

I need to insert multiple chars into a database table, the code below inserts one random char(in two different ways) in every table row. But i need like 10 different chars in every row. How can i do that?

public static void insertToTable2(Connection c, String tableName, int numberOfRows) throws UnsupportedEncodingException, SQLException {
            Random rand = new Random();
            String chars = "abcdf";
            StringBuilder sql =
                    new StringBuilder("INSERT INTO " + tableName + " (NR,PIRMAS1,ANTRAS1,TRECIAS1,KETVIRTAS1,PENKTAS1,SESTAS1,SEPTINTAS1,ASTUNTAS1,DEVINTAS1) VALUES ");

            for (int j=0; j < numberOfRows; j++)
            {
                if (j != 0) sql.append (",");
                sql.append ("(" + j +
                        ",'" + chars.charAt(rand.nextInt(chars.length())) + "'" +
                        ",'" + chars.charAt(rand.nextInt(chars.length())) + "'" +
                        ",'" + (char)(rand.nextInt(25)+65) + "'" +
                        ",'" + (char)(rand.nextInt()) + "'" +
                        ",'" + (char)(rand.nextInt()) + "'" +
                        ",'" + (char)(rand.nextInt()) + "'" +
                        ",'" + (char)(rand.nextInt()) + "'" +
                        ",'" + (char)(rand.nextInt()) + "'" +
                        ",'" + (char)(rand.nextInt()) + "'" +
                        ")") ;


            }