Why is it not in the order of key when converting key to uppercase even though I use LinkedHashMap

Question

When I convert to lowercase, it's in the right order. When I try to convert to uppercase,it's wrong. I try to use LinkedHashMap to keeping the insertion order. I think stream changed the order of keys,But I don't know how to sort after changing the key.

Thanks in advance.

Here is my code



import java.util.*;
import java.util.stream.Collectors;

public class Test {

    static List>  convertKeyCase (List> list,int...s) {

       return list.stream().map(m -> m.entrySet().stream().sorted(Map.Entry.comparingByKey())
               .collect(Collectors.toMap(p -> s.length == 0 || s[0]==1 ? p.getKey().toUpperCase():p.getKey().toLowerCase(), Map.Entry::getValue)))
               .collect(Collectors.toList());

    }
    public static void main(String[] args) {
        List> list1 = new ArrayList<>();

        Map map1 = new LinkedHashMap<>();
        Map map2 = new LinkedHashMap<>();


        map1.put("date","2021-06-03");
        map1.put("weather","1");
        map1.put("wind","2-3");
        map1.put("temp","17-29°C");
        list1.add(map1);

        map2.put("date","2021-06-04");
        map2.put("weather","1");
        map2.put("wind","3-4");
        map2.put("temp","17-30°C");
        list1.add(map2);

        List> list = convertKeyCase(list1);
        List> list2 = convertKeyCase(list1,0);
        System.out.println(list);
        System.out.println(list2);

    }
}

user_1221571 · Answer

The fact that the input List contains LinkedHashMaps doesn't mean that the output will contain LinkedHashMaps.

If you want LinkedHashMaps, you must request them explicitly in the toMap() call:

static List>  convertKeyCase (List> list,int...s) {

   return list.stream()
              .map(m -> m.entrySet()
                         .stream()
                         .sorted(Map.Entry.comparingByKey())
                         .collect(Collectors.toMap(p -> s.length == 0 || s[0]==1 ? p.getKey().toUpperCase():p.getKey().toLowerCase(),
                                                   Map.Entry::getValue,
                                                   (v1,v2)->v1,
                                                   LinkedHashMap::new)))
              .collect(Collectors.toList());

}

This changes the output to:

[{DATE=2021-06-03, TEMP=17-29°C, WEATHER=1, WIND=2-3}, {DATE=2021-06-04, TEMP=17-30°C, WEATHER=1, WIND=3-4}]
[{date=2021-06-03, temp=17-29°C, weather=1, wind=2-3}, {date=2021-06-04, temp=17-30°C, weather=1, wind=3-4}]

user_1869846 · Answer

After below two lines again you will get a List and natural sorting will be applied. You have to change your implementation to return LinkedHashMap there.

    List> list = convertKeyCase(list1);
    List> list2 = convertKeyCase(list1,0);

Why is it not in the order of key when converting key to uppercase even though I use LinkedHashMap

2 Answers