java - Firebase returning keys of child node in different orders on different devices/Android versions

Question

I am getting a snapshot of the data from my Firebase database to retrieve a users list, but the order of the keys being returned is different depending on the Android version/ device being used.

For demonstrative purposes I have shortened the method, but it is essentially as follows:

public void getUsers(){
    Firebase ref = new Firebase("https://myFirebaseID.firebaseio.com");
    final Firebase userRef = ref.child("users");

    userRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot snapshot) {
           snapshot.toString();
        }                                                           
    });
}

It is the data I get from calling toString() on the snapshot object (snapshot.toString()) that changes order.

I have tried it on 4 devices. The 2 running Lollipop (Nexus 7 5.1.1 & Galaxy s4 5.01) return the data in the same order. And the 2 two other devices (HTC Sensation 4.0.3 and Motorola G2 4.4.4) return the data in the same order (but a different order to devices with Lollipop).

There is no difference in the code used, and the data in the database was completely unchanged at the times when I retrieved the snapshots.

Here is the data order on the 4.4.4 and 4.0.3 devices:

DataSnapshot { 
  key = users, 
  value = {
    114585619420240714499={
      **userIDOfCUser**=114585619420240714499,
      **NameOfCUser**=testName,
      **EmailOfCUser**[email protected],
      **friends**={
        103902248954972338254={
          **userIDOfFriend**=103902248954972338254, 
          **NameOfFriend**=testName2 
        }
      }
    }  

Here is the data order on the 5.1.1 and 5.01 devices:

DataSnapshot { 
  key = users, 
  value = {
    114585619420240714499={
      **NameOfCUser**=testName, 
      **userIDOfCUser**=114585619420240714499, 
      **friends**={
        103902248954972338254={
          **NameOfFriend**=testName2 ,
          **userIDOfFriend**=103902248954972338254
        }
      }, 
      **EmailOfCUser**= [email protected]
    }
  }
}

Why is the data being delivered in different orders depending on the android version/device being used? is there another difference I am unaware of?

Edit: When iterating through the snapshot as follows, the different ordering of the keys still persists accross different versions of Android:

public void getUsers2(){

  Firebase ref = new Firebase("https://myFirebaseID.firebaseio.com");
  final Firebase userRef = ref.child("users");
  userRef.addListenerForSingleValueEvent(new ValueEventListener() {

    @Override
    public void onDataChange(DataSnapshot snapshot) {
        for (DataSnapshot keys : snapshot.getChildren()) {
            //String to temporarily store the whole child of the inidividual user's DB node ----> It still produces different order of the keys 
            String tempKey = keys.getValue().toString();

            //The problem persists if I code it like this as well. 
            String tempKey2 = snapshot.child(keys.getKey()).getValue().toString();

        }
    }
  });
}

Answer 1

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