Why Map in Apex is auto sort key?

Question

I have code below

public class LearnAboutMap {
     public LearnAboutMap () {
          Map<String, String> m = new Map<String, String>();
          m.put('Type', '1');
          m.put('Contact', '1');
          m.put('Additional', '1');
          m.put('Supper', '1');
          m.put('Body', '1');
          System.debug(m);

          //Output: {Additional=1, Body=1, Contact=1, Supper=1, Type=1}
          //Expected: {Type=1, Contact=1, Additional=1, Supper=1, Body=1}
     }

}

Why Map in Apex is auto sort key ?

Answer 1

Since you want Map keys to be iterated in the order you placed in the Map. So convert the Map.keySet() to List and it will be sorted.

Map<String, String> m = new Map<String, String>();
m.put('Type', '1');
m.put('Contact', '1');
m.put('Additional', '1');
m.put('Supper', '1');
m.put('Body', '1');
System.debug(new List<String>(m.keySet()));

12:04:32:003 USER_DEBUG [7]|DEBUG|(Type, Contact, Additional, Supper, Body)

Answer 2

Not sure if this answers your question, but here's what the docs say on how they are implemented:

Apex uses a hash structure for all maps, and the The iteration order of map elements is deterministic. You can rely on the order being the same in each subsequent execution of the same code. However, SF recommends to always access map elements by key.

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/langCon_apex_collections_maps.htm

Answer 3

You're looking at the internal stringified representation of the map that is made available to you for debug purposes. The Map class does not specify the order of keys, there's no "auto sort". Deterministic ordering is only guaranteed on map's elements via values() method.