Java Collator unexpected output

Question

I need to compare strings in my program without considering special national characters, so e.g. "C" and "Č" should be the same. I used Collator class. For first and second case it works like expected, but in third and fourth case no.

package collator;

import java.text.Collator;
import java.util.Locale;

public class Coll {

public static void main(String[] args) {
    Locale locale = new Locale("sk", "SK");
    Collator collator = Collator.getInstance(locale);
    collator.setStrength(Collator.PRIMARY);
    System.out.println(collator.compare("T", "Ť"));
    System.out.println(collator.compare("L", "Ľ"));
    System.out.println(collator.compare("C", "Č"));
    System.out.println(collator.compare("S", "Š"));
    }
}

I expect 0 0 0 0, but actual output is 0 0 -1 -1

Answer 1

Check out the java.text.Normalizer class. I have never used it extensively but it looks like it could be useful for your purpose. Example:

import java.text.Normalizer;
import java.text.Normalizer.Form;

public class NewClass2 {

    public static void main(String[] args) {

        System.out.println("T".compareTo( normalizeString("Ť") ));
        System.out.println("L".compareTo( normalizeString("Ľ") ));
        System.out.println("C".compareTo( normalizeString("Č") ));
        System.out.println("S".compareTo( normalizeString("Š") ));
        System.out.println("O".compareTo( normalizeString("Ö") ));
        System.out.println("U".compareTo( normalizeString("Ü") ));
        System.out.println("A".compareTo( normalizeString("Ä") ));
        System.out.println("A".compareTo( normalizeString("Å") ));        
    }

    public static String normalizeString(String str){
        return Normalizer.normalize(str, Form.NFD).replaceAll("[^\\p{ASCII}]", "");
    }
}

Read this blog post for more information: normalizing-text-in-java