Sorting a entrySet by keys

Question

In my entrySet I have the next values:

name -> "someName"
nameSpace -> "someNameSpace"
version -> "someVersion"

I'm iterating over this entrySet and adding its values to a final object, my problem is that I need to add the values in the order:

nameSpace -> "someNameSpace"
name -> "someName"
version -> "someVersion"

With nameSpace first. Not pretty sure if it's possible to achieve that using a stream or something more sophisticated. I'm doing the process manually.

public static void main(String [] args){
     SortedMap<String, String> coordinates = new TreeMap<>();
    coordinates.put("name", "nameValue");
    coordinates.put("nameSpace", "nameSpaceValue");
    coordinates.put("version", "versionValue");
    String name = coordinates.get("name");
    String nameSpace = coordinates.get("nameSpace");
    String version = coordinates.get("version");

    /*Object.add("name", name);
    Object.add("nameSpace", nameSpace);
    Object.add("version", version);*/
}

Thanks!

Iterate over the map, add each of them to a list, then sort the list as you wish. — Romain Hippeau, Oct 21 '21 at 16:35

score 1 · Answer 1 · answered Oct 21 '21 at 17:15

It seems natural sorting is not applicable to the keys in this specific order: nameSpace, name, version, therefore SortedMap / TreeMap would require some very custom/hardcoded comparator:

SortedMap<String, String> coordinates = new TreeMap<>(
    (a, b) -> b.startsWith(a) && !a.startsWith(b) ? 1 : a.compareTo(b)
);
coordinates.put("version", "versionValue");
coordinates.put("nameSpace", "nameSpaceValue");
coordinates.put("name", "nameValue");

// iterating the map
// coordinates.forEach((k, v) -> Object.add(k, v));
coordinates.forEach((k, v) -> System.out.println(k + " -> " + v));

Output:

nameSpace -> nameSpaceValue
name -> nameValue
version -> versionValue

Another approach would be to use LinkedHashMap capable of maintaining the insertion order and fix this order as necessary:

Map<String, String> coordinates = new LinkedHashMap<>();
// add entries in expected order
coordinates.put("nameSpace", "nameSpaceValue");
coordinates.put("name", "nameValue");
coordinates.put("version", "versionValue");

Similar approach would be to use an unsorted map and a list of keys in the desired order.

Map<String, String> coordinates = new HashMap<>();    
coordinates.put("name", "nameValue");
coordinates.put("nameSpace", "nameSpaceValue");
coordinates.put("version", "versionValue");

List<String> keyOrder = Arrays.asList("nameSpace", "name", "version");
keyOrder.forEach(k -> System.out.println(k + " -> " + coordinates.get(k)));

However, it seems that method add of the custom object requires both key and value anyway, so the order of populating the fields should not be relevant.

Sorting a entrySet by keys

1 Answers1