public static boolean isDiscover(String cc) {
        String first4digs = cc.substring(0, 4);

        if ((cc.length() == 16) && (first4digs.equals("6011")))
            return isCreditCard(cc);
        return false;
    }
public static boolean isDiscover ( String cc ) { String first4digs = cc . substring ( 0 , 4 ) ; if ( ( cc . length ( ) == 16 ) && ( first4digs . equals ( "6011" ) ) ) return isCreditCard ( cc ) ; return false ; }
Checks to see if the cc number is a valid Discover number
@param    cc - a string representing a credit card number; Sample number: 6011000000000004(16 digits)
@return  true, if the credit card number is a valid Discover card number, false otherwise