java ArrayList retrieving highest value

Question

Executing this code should outcome number 6 since i am only retrieving two values from Data.snapshot [3,6]. but i keep getting both of them in this form : [3,6]. Is there something i am doing wrong or my understanding of the extracted snapshot and the HashMap is not correct, and how could i get the highest value ?

     public void ratingCount(){
    Firebase ref = new Firebase("https://CLOUD_NAME.firebaseio.com/rating/"+UserID);
    ref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot snapshot) {
            Map<String, String> ratings = (HashMap<String,String>) snapshot.getValue();
            Collection<String> BulkValues = ratings.values();
            ArrayList <String> values = new ArrayList<>();
            values.add(BulkValues.toString());
            Comparator<String> compare = new Comparator<String>() {
                @Override
                public int compare(String lhs, String rhs) {
                    return Integer.valueOf(lhs).compareTo(Integer.valueOf(rhs));
                }
            };
                textViewRatingValue.setText(Collections.max(values, compare));
        }
        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });
}

Applying Erans suggestion, the code is ;

             public void onDataChange(DataSnapshot snapshot) {
            Map<String, String> ratings = (HashMap<String,String>) snapshot.getValue();
            Collection<String> BulkValues = ratings.values();
            ArrayList <String> values = new ArrayList<>(BulkValues);
            Comparator<String> compare = new Comparator<String>() {
                @Override
                public int compare(String lhs, String rhs) {
                    return Integer.valueOf(lhs).compareTo(Integer.valueOf(rhs));
                }
            };
                textViewRatingValue.setText(Collections.max(values, compare));
}

and the Error :

 04-06 13:07:37.353 31832-31832/net.we4x4.we4x4 E/AndroidRuntime: FATAL EXCEPTION: main
                                                             Process: net.we4x4.we4x4, PID: 31832
                                                             java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.String
                                                                 at net.we4x4.we4x4.MyInformation$7$1.compare(MyInformation.java:259)
                                                                 at java.util.Collections.max(Collections.java:1629)
                                                                 at net.we4x4.we4x4.MyInformation$7.onDataChange

Is it because it is still being treated as one single String [3,6] and cant be compared ? or because i am passing it to textView " textViewRatingValue " in a wrong way ?

Well, Thanks to Eran precise explanation, the retrieved data is "Long" thus it must be indicated as so, that was the second mistake i was doing, and doing so getting the max is simpler as following;

                Map<Long, Long> map = (HashMap<Long, Long>) snapshot.getValue();
            Map<Long, Long> ratings = map;
            Collection<Long> BulkValues = ratings.values();
            ArrayList<Long> values = new ArrayList<>();
            values.addAll(BulkValues);

            Long max = Collections.max(values);
            textViewRatingValue.setText(max.toString());
        }

Eran · Accepted Answer · 2016-04-06 08:33:08Z

2

You are adding a single element to values, which is the String representation of that Collection (the String "[3,6]" in your case) :

values.add(BulkValues.toString());

If you want to add all the elements, use :

values.addAll(BulkValues);

or just declare values as :

ArrayList <String> values = new ArrayList<>(BulkValues);

answered Apr 6, 2016 at 8:33

Eran

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7 Comments

madnomad10011 Over a year ago

Your explanation make sense, but i encountered an error applying it as you could see in my updates of main thread ? is it because the HashMap <String, String> snapshot, is a single extracted as a single String and cant be compared ?

madnomad10011 Over a year ago

you are too fast, check again LOL. Plus i've tried "venu" suggestion but i see in his code he did not consider the fact that i am receiving the data from firebase as a snapshot,which i guess it is an object, and i am not inputing the data in my own, so i tried to use his code, but i was not sure how to do so, and if i did it correctly ?

Eran Over a year ago

@JanusJanus The error you got implies that the value in the snapshot Map is Long, not String, so casting it to (HashMap<String,String>) is probably wrong. You should check the actual runtime types you are getting, and use the correct types in your code.

madnomad10011 Over a year ago

i hope you could patient with me hear, since i am not that familiar with several things, how could i check the runtime types ? and even when i tried to change all the " String " in the code to Long, at the end i get an red underline the "compare" in : textViewRatingValue.setText(Collections.max(values, compare));

Eran Over a year ago

@JanusJanus If values is a List<Long> you don't need the Comparator. Just use Collections.max(values).

|

Venu · Accepted Answer · 2016-04-06 09:12:15Z

1

Here you are adding total array as a string (values.add(BulkValues.toString())). instead of that you need to use addAll like this values.addAll(BulkValues);

See below example.

Map<String, String> map=new HashMap<>();
            map.put("one", "1");
            map.put("six", "6");
            map.put("three", "3");
            map.put("nine", "9");
            map.put("seven", "7");
             Map<String, String> ratings =map;
             Collection<String> BulkValues = ratings.values();
             ArrayList <String> values = new ArrayList<>();
             values.addAll(BulkValues);

             Comparator<String> compare = new Comparator<String>() {
                 @Override
                 public int compare(String lhs, String rhs) {
                     return Integer.valueOf(lhs).compareTo(Integer.valueOf(rhs));
                 }
             };

             System.out.println(Collections.max(values, compare));
            }

output:

Hope it will help you.

edited Apr 6, 2016 at 9:12

answered Apr 6, 2016 at 9:05

Venu

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3 Comments

madnomad10011 Over a year ago

i've tried your suggestion but i am receiving the data from firebase as a snapshot,which i guess it is an object, so am not sure how pass the data, and if i did it correctly ?

Venu Over a year ago

@JanusJanes Sorry i didn't observe properly. Here i guess snapshot.getValue() returns Hashmap object with long values but you are assigning to Hashmap<String,String> this is wrong.. So you need to do like this (Hashmap<String,Long>) ratings.value();

madnomad10011 Over a year ago

Yes, Thank you @venu, worked now, and understood the concept.

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