What should I change in my code to sort city names, but it has non english letters too?

Question

Code works. It sorts from A to Z. But there are Ç, İ etc. They come after Z which is wrong.

Here is the code

KeyValueDTO.java

public class KeyValueDTO implements Comparable<KeyValueDTO> {
    private String key;
    private String value;

    
    public String getKey() {
        return key;
    }

    public void setKey(String key) {
        this.key = key;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "KeyValueDTO [key=" + key + ", value=" + value + "]";
    }
    
    @Override
    public int compareTo(KeyValueDTO other) {
        return key.compareTo(other.key);
    }
    
    /*
    public int compare(KeyValueDTO s1, KeyValueDTO s2) {
        Collator collator = Collator.getInstance(new Locale("tr", "TR"));
        return collator.compare(s1, s2);
    }*/
    
}

Controller

@RequestMapping(value = "/getCities", method = RequestMethod.GET)
    @Cacheable("cities")
    public @ResponseBody List<KeyValueDTO> getCities() {
        logger.trace("getCities begins.");
        List<City> cityList = cityService.findAll();
        List<KeyValueDTO> cityKeyDtoList = new ArrayList<KeyValueDTO>();
        

        for (City city : cityList) {
            KeyValueDTO cityKeyDto = new KeyValueDTO();
            cityKeyDto.setKey(city.getName());
            cityKeyDto.setValue(String.valueOf(city.getCode()));
            cityKeyDtoList.add(cityKeyDto);
            
        }
        Collections.sort(cityKeyDtoList);
        // Collections.sort(cityKeyDtoList,Collator.getInstance(new Locale("tr", "TR")));

        logger.trace("CityController: getAllCities ends");
        return cityKeyDtoList;
    }

it works from A to Z, but not Ç İ.. I tried to add Collactor i couldnt use it right way. Could u do some help please?

I wrote this but it doesnt work. It stops running on eclipse.

public @ResponseBody List<KeyValueDTO> getCities() {
        logger.trace("getCities begins.");
        List<City> cityList = cityService.findAll();
        List<KeyValueDTO> cityKeyDtoList = new ArrayList<KeyValueDTO>();
        
        Locale turkish = new Locale("tr", "TR");
        Collator collator = Collator.getInstance(turkish);
        
        for (City city : cityList) {
            KeyValueDTO cityKeyDto = new KeyValueDTO();
            cityKeyDto.setKey(city.getName());
            cityKeyDto.setValue(String.valueOf(city.getCode()));
            cityKeyDtoList.add(cityKeyDto);
            
        }
        //Collections.sort(cityKeyDtoList);
        // Collections.sort(cityKeyDtoList,Collator.getInstance(new Locale("tr", "TR")));
        Collections.sort(cityKeyDtoList, collator);


        logger.trace("CityController: getAllCities ends");
        return cityKeyDtoList;
    }

Answer 1

You have Ç and İ in your data. Let's assume it is Turkish.

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

Locale turkish = new Locale("tr", "TR");
Collator collator = Collator.getInstance(turkish);
Collections.sort(cityKeyDtoList, collator)

Example outcome is given above. Don't mind the class name, non-relevant.

---

ALTERNATIVE SOLUTION

Changed from Comparable to Comparator.

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

public class KeyValueDTO{
    private String key;
    private String value;

    
    public String getKey() {
        return key;
    }

    public void setKey(String key) {
        this.key = key;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "KeyValueDTO [key=" + key + ", value=" + value + "]";
    }
    
    public Comparator<KeyValueDTO> comparisonOrder() {
        return new CustomComparator();
    }
    private class CustomComparator implements Comparator<KeyValueDTO> {

        @Override
        public int compare(KeyValueDTO o1, KeyValueDTO o2) {
            Collator collator = Collator.getInstance(new Locale("tr", "TR"));
            return collator.compare(o1.getKey(), o2.getKey());
        }
        
    }

}

example main:

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;


public class Solution {
    public static void main(String[] args ) {
        KeyValueDTO city1= new KeyValueDTO();
        city1.setKey("Adana");
        KeyValueDTO city2= new KeyValueDTO();
        city2.setKey("İstanbul");
        KeyValueDTO city3= new KeyValueDTO();
        city3.setKey("Zonguldak");
        KeyValueDTO city4= new KeyValueDTO();
        city4.setKey("Çanakkale");
        
        List<KeyValueDTO> cityKeyDtoList = new ArrayList<KeyValueDTO>();
        cityKeyDtoList.add(city1);
        cityKeyDtoList.add(city2);
        cityKeyDtoList.add(city3);
        cityKeyDtoList.add(city4);
        
        
        Collections.sort(cityKeyDtoList, city1.comparisonOrder());
        System.out.println(cityKeyDtoList.toString());
    }
}