Strange behaviour while reading array in Android-Java

Question

I'm trying to get array of int values from JSON, however something strange is happening and i get different output when i read the same array on two places in the code.

Does anyone know the reason behind this behaviour?

public LineGraphSeries<DataPoint> fillGraph(String city, int numberOfDays){
    int data[] = new int[numberOfDays*8];
    DataPoint[] temperatures = new DataPoint[numberOfDays*8];
    LineGraphSeries<DataPoint> graph;
    String url = "http://api.worldweatheronline.com/free/v2/weather.ashx?q=" + city + "&format=json&num_of_days=" + numberOfDays + "&cc=no&fx24=no&show_comments=no&tp=3&key=e74975c820b1f6506bd6b9fdea5a5";
    JSONObject dataZNetu;
    JSONArray dataArray;
    JSONObject dataHourly;
    JSONArray dataHourlyArray;
    try {
        dataZNetu = requestWebService(url).getJSONObject("data");
        dataArray = dataZNetu.getJSONArray("weather");
        for(int i = 0; i<dataArray.length(); i++){
            dataHourly = dataArray.getJSONObject(i);
            dataHourlyArray = dataHourly.getJSONArray("hourly");
            for(int j = 0; j<dataHourlyArray.length(); j++){
                data[i*j] = dataHourlyArray.getJSONObject(j).getInt("FeelsLikeC");
                //temperatures[i*j] = new DataPoint(i*j,data[i*j]);
                Log.v("dataCorrect" + i,String.valueOf(data[i*j])); //Correct values
            }
        }
    }
    catch (Exception e) {
        e.printStackTrace();
    }
    for(int i = 0;i<data.length;i++){
        Log.v("dataBroken" + i/8,String.valueOf(data[i])); //Broken values
    }

    graph = new LineGraphSeries<DataPoint>(temperatures);
    return graph;
}

Log:

05-15 02:05:50.609  13125-13125/com.example.tomus.weatherdresser V/dataCorrect0﹕ 6

05-15 02:05:50.609  13125-13125/com.example.tomus.weatherdresser V/dataCorrect0﹕ 5

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect0﹕ 12

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect0﹕ 18

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect0﹕ 19

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect0﹕ 20

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect0﹕ 16

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect0﹕ 14

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect1﹕ 10

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect1﹕ 7

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect1﹕ 16

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect1﹕ 20

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect1﹕ 24

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect1﹕ 24

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect1﹕ 18

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect1﹕ 15

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect2﹕ 11

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect2﹕ 11

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect2﹕ 15

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect2﹕ 16

05-15 02:05:50.619  13125-13125/com.example.tomus.weatherdresser V/dataCorrect2﹕ 17

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataCorrect2﹕ 17

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataCorrect2﹕ 14

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataCorrect2﹕ 11

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken0﹕ 11

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken0﹕ 7

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken0﹕ 11

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken0﹕ 20

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken0﹕ 15

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken0﹕ 24

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken0﹕ 16

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken0﹕ 15

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken1﹕ 17

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken1﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken1﹕ 17

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken1﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken1﹕ 14

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken1﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken1﹕ 11

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken1﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken2﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken2﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken2﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken2﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken2﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken2﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken2﹕ 0

05-15 02:05:50.629  13125-13125/com.example.tomus.weatherdresser V/dataBroken2﹕ 0

data[i*j]??? Are you sure? Maybe you mean something like data[(i*8)+j]? Whatever - your indexing arithmetic is completely different between the "Correct: and "Broken" examples :( — paulsm4
– paulsm4, Commented May 15, 2015 at 0:19
I think he meant i*dataHourlyArray.length()+j. Of course even that may be wrong if dataHourlyArray.length() isn't a constant for all indexes in dataArray — Gabe Sechan
– Gabe Sechan, Commented May 15, 2015 at 0:21
thanx, it was bad indexing as FoggyDay described... never work too long into night guys. — Tomus
– Tomus, Commented May 15, 2015 at 9:11

Christian Abella · Accepted Answer · 2015-05-15 03:00:01Z

1

You need to change your array declaration as well as the way you are accessing it. Instead of using * or multiplication during initialization, just a multi-dimension array and use [][] instead of performing arithmetic operation on the array.

 int [][]data = new int[numberOfDays][8];
 String url = "http://api.worldweatheronline.com/free/v2/weather.ashx?q=" + city + "&format=json&num_of_days=" + numberOfDays + "&cc=no&fx24=no&show_comments=no&tp=3&key=e74975c820b1f6506bd6b9fdea5a5";
 JSONObject dataZNetu;
 JSONArray dataArray;
 JSONObject dataHourly;
 JSONArray dataHourlyArray;
    try
    {
      WebContext webContext = new WebContext();
      dataZNetu = webContext.DownloadJSON(url).getJSONObject("data");
      dataArray = dataZNetu.getJSONArray("weather");
      for(int i = 0; i<dataArray.length(); i++)
      {
        dataHourly = dataArray.getJSONObject(i);
        dataHourlyArray = dataHourly.getJSONArray("hourly");
        for(int j = 0; j<dataHourlyArray.length(); j++){
          data[i][j] = dataHourlyArray.getJSONObject(j).getInt("FeelsLikeC");
          //temperatures[i*j] = new DataPoint(i*j,data[i*j]);
          Log.v("dataCorrect" + i,String.valueOf(data[i][j])); //Correct values
        }
      }
    }
    catch (Exception e)
    {
      e.printStackTrace();
    }
    for(int i = 0;i<data.length;i++)
    {
      Log.v("dataBroken" + i/8,String.valueOf(data[i])); //Broken values
    }

answered May 15, 2015 at 3:00

Christian Abella

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1 Comment

Tomus Over a year ago

Is it a general rule of thumb to add a dimension instead of performing arithmetic? Seems safer, but i have never been recommended to use this approach. Anyway, your solution would allso solve this situation as it will make the code easier to grasp. Thanx

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