String input = "";
        String phoneNumber = "";
        boolean valid = true;

        Scanner keyboard = new Scanner(System.in);

        while(valid == true)
        {
            System.out.println("Please write a tellephone to know if it is valid");
            input = keyboard.next();

            if("exit".equals(input))
            {
                break;
            }

            for(int cont = 0; cont != input.length(); cont ++)
            {
                if(input.charAt(cont) != '(' && input.charAt(cont) != ')' && input.charAt(cont) != '-')
                {
                    phoneNumber = phoneNumber + input.charAt(cont);
                }
            }
            float phone;
            try
            {
                phone = Float.parseFloat(phoneNumber);
                if(phoneNumber.length() == 10)
                {
                    System.out.println("It is valid!");
                }
                else
                {
                    System.out.println("It is invalid!");
                }
            }
            catch(NumberFormatException ex)
            {
                System.out.println("It is invalid!");
            }
        }