Map.keySet() read sequence?

Question

I have Map<String, List<String>> map now, putting two values inside Map, now when read keyset from map gives in different sequence in different device.

private Map<String, List<String>>  map = new HashMap<>();

map.put("First", new ArrayList<String>());
map.put("Second", new ArrayList<String>());

Now, Read keys from this map.

 Set<String> keys = map.keySet();

 for (int i = 0; i < map.size(); i++) {
     Log.d("key", keys.toArray()[i].toString());
 }

OUTPUT IN OREO 8.0

D/Key : First
D/Key : Second

OUTPUT in BELOW 8.0

D/Key : Second
D/Key : First

Um, a `Set` has no defined order. You are getting a `Set` from `keySet()`; you should make no assumptions at all about the order of elements in that `Set`. — CommonsWare, Mar 26 '18 at 12:36
yeah , but how it is possible to read it in different order basically it;s happen in only in Oreo 8 — Vishal Patoliya ツ, Mar 26 '18 at 12:38
Again, you should make no assumptions at all about the order of elements in that `Set`. If you want them to be in some order, convert the `Set` to an `ArrayList`, then sort the `ArrayList` by your desired order. — CommonsWare, Mar 26 '18 at 12:39
@CommonsWare maven { url "https://s3.amazonaws.com/repo.commonsware.com" } this is take too much time for compile is there any solution ? — Vishal Patoliya ツ, Mar 29 '18 at 07:26
Have you develop this Lib url "s3.amazonaws.com/repo.commonsware.com ?? — Vishal Patoliya ツ, Mar 29 '18 at 12:04
Thanks Can you please tell me that whenever i change something in gradle its download every time and it is too time consuming so, have you any solution ? @CommonsWare — Vishal Patoliya ツ, Mar 29 '18 at 12:19
what is alternate of this ? Are you working at Google / Amazon @CommonsWare ? — Vishal Patoliya ツ, Mar 29 '18 at 12:31

score 1 · Accepted Answer · answered Mar 26 '18 at 12:51

1

I got a solution until we defined Set as SortedSet ,we getting key sequence in different order.

SortedSet<String> keys =  new TreeSet<>(map.keySet());

for (int i = 0; i < map.size(); i++) {
    Log.d("key", keys.toArray()[i].toString());            
}

answered Mar 26 '18 at 12:51

Vishal Patoliya ツ

3,170
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mark42inbound · Answer 2 · 2018-03-26T13:21:39.440

You're using the HashMap as the data structure. As in HashMap, the order of insertion is not maintained thus you're getting a random order of the keys. If you want to maintain the order of insertion, simply use a LinkedHashMap. The order in which you put the data is maintained and simply you can iterate over it.

Sample code for LinkedHashMap:

Map<String, String> map = new LinkedHashMap<>();
    map.put("key1", "value2");
    map.put("key3", "value4");
    map.put("key5", "value6");
    map.put("key7", "value8");
    Set<String> keySet = map.keySet();
    for(String st: keySet){
        System.out.println(st);
    }
    for(Map.Entry<String, String> entry : map.entrySet()){
        System.out.println(entry.getKey() + " " + entry.getValue());
    }

Output:

key1
key3
key5
key7
key1 value2
key3 value4
key5 value6
key7 value8

score 0 · Answer 3 · answered Mar 26 '18 at 12:41

0

It has nothing to do with the android OS. The resulting Set of HashMap has no order. However there are Sets with an order e.g. TreeSet.

answered Mar 26 '18 at 12:41

Murat Karagöz

35,401
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Map.keySet() read sequence?

3 Answers3