> Roman, thank you for your help. But i changed my code. Now no
> exception but some special Turkish characters like '?' this in
> database.
>
> Connection conn = DriverManager.getConnection
> ("jdbc:firebirdsql:localhost/3050:" + database + "?user=" + user
> + "&password=" + password + "&encoding=WIN1254");

I suspect other thing - they are not "?" in database, but normal Turkish
characters. However your application is not displaying them correctly. To
check this, simply print the character codes of the string you get from DB
to the console:

String myStr = rs.getString(1);
char[] chars = myStr.toCharArray();

for(int i = 0; i < chars.length; i++) {
System.out.println("chars[" + i + "] = " + ((int)chars[i]));
}

Please note the casting of char to int, if you do not do this, you will see
characters, not their codes.

Roman