Using Locales with Java's toLowerCase() and toUpperCase()

I think you should use locale ,

For instance, "TITLE".toLowerCase() in a Turkish locale returns "tıtle", where 'ı' is the LATIN SMALL LETTER DOTLESS I character. To obtain correct results for locale insensitive strings, use toLowerCase(Locale.ENGLISH).

I refer to these links as solution to your problem and it has point to keep in mind in you situation "Turkish"

**FROM THE LINKS**

toLowerCase() respects internationalization (i18n). It performs the case conversion with respect to your Locale. When you call toLowerCase(), internally toLowerCase(Locale.getDefault()) is getting called. It is locale sensitive and you should not write a logic around it interpreting locale independently.

import java.util.Locale;
 
public class ToLocaleTest {
    public static void main(String[] args) throws Exception {
        Locale.setDefault(new Locale("lt")); //setting Lithuanian as locale
        String str = "\u00cc";
    System.out.println("Before case conversion is "+str+
" and length is "+str.length());// Ì
        String lowerCaseStr = str.toLowerCase();
    System.out.println("Lower case is "+lowerCaseStr+
" and length is "+lowerCaseStr.length());// iı`
    }
}

In the above program, look at the string length before and after conversion. It will be 1 and 3. Yes the length of the string before and after case conversion is different. Your logic will go for a toss when you depend on string length on this scenario. When your program gets executed in a different environment, it may fail. This will be a nice catch in code review.

To make it safer, you may use another method toLowerCase(Locale.English) and override the locale to English always. But then you are not internationalized.

So the crux is, toLowerCase() is locale specific.

reference 1
reference 2
reference 3

Dotless-i, is a lowercase 'i' without dot. The uppercase of this character is the usual "I". There is another character, "I with dot". The lowercase of this character is the usual lowercase "i".

Have you noticed the problem? This unsymetrical conversion causes a serious problem in programming. We face this problem mostly in Java applications because of (IMHO) poor implementation of toLowerCase and toUpperCase functions.

In Java, String.toLowerCase() method converts characters to lowercase according to the default locale. This causes problems if your application works in Turkish locale and especially if you are using this function for a file name or a url that must obey a certain character set.

I have blogged about two serious examples before: The compile errors with Script libraries with "i" in their names and XSP Manager's fault if an XPage is in a database with "I" in its name.

There is a long history, as I said. For instance in some R7 version, router was unable to send a message to a recipient if his/her name starts with "I". Message reporting agents was not running in Turkish locale until R8. Anyone with Turkish locale could not install Lotus Notes 8.5.1 (it's real!). The list goes on...

There is almost no beta tester from Turkey and customers don't open PMR for these problems. So these problems are not going up to the first priority for development teams.

Even Java team has added a special warning to the latest documentation:

This method is locale sensitive, and may produce unexpected results if used for strings that are intended to be interpreted locale independently. Examples are programming language identifiers, protocol keys, and HTML tags. For instance, "TITLE".toLowerCase() in a Turkish locale returns "tıtle", where 'ı' is the LATIN SMALL LETTER DOTLESS I character. To obtain correct results for locale insensitive strings, use toLowerCase(Locale.ENGLISH).

You can create appropriate locale for your String's language.

For example:

toUpperCase(new Locale("tr","TR"));

will do the trick for Turkish.