Calculate max from ArrayList not working

Question

public class GraphFrameV2 extends Fragment implements AdapterView.OnItemSelectedListener {
    Integer hoodSelector = 27;
    ArrayList<HoodData> hoodDataList = new ArrayList<>();
    ArrayList<String> hoodList = new ArrayList<>();
    ArrayList<HoodData> completeHoodList = new ArrayList<>();

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        String item = parent.getItemAtPosition(position).toString();
        // Showing selected spinner item
        for(int i = 1; i < hoodList.size(); i++) {
            if (item.equals(hoodList.get(i))) {
                setHoodId(i + 27);
                refreshFragment();
            }

        }
    }
    public Double calculateMax(Integer year){
        Double max = completeHoodList.get(0).getPercentage();
        if(year == 2006){
            for(Integer z = 0; z < completeHoodList.size(); z ++){
                if(completeHoodList.get(z).getYear() == 2006){
                    if(completeHoodList.get(z).getPercentage() > max){
                        max = completeHoodList.get(z).getPercentage();
                    }
                }
            }
        }
        Toast.makeText(getActivity(), String.valueOf(max),
                Toast.LENGTH_LONG).show();
        return max; 
    }
    public void calculateMin(Integer year){
        Double min = completeHoodList.get(0).getPercentage();
        if(year == 2006){
            for(Integer z = 0; z < completeHoodList.size(); z ++){
                if(completeHoodList.get(z).getYear() == 2006){
                    if(completeHoodList.get(z).getPercentage() < min){
                        min = completeHoodList.get(z).getPercentage();
                    }
                }
            }
        }
        if(year == 2007){
            for(Integer z = 0; z < completeHoodList.size(); z ++){
                if(completeHoodList.get(z).getYear() == 2007){
                    if(completeHoodList.get(z).getPercentage() < min){
                        min = completeHoodList.get(z).getPercentage();
                    }
                }
            }
        }
        if(year == 2008){
            for(Integer z = 0; z < completeHoodList.size(); z ++){
                if(completeHoodList.get(z).getYear() == 2008){
                    if(completeHoodList.get(z).getPercentage() < min){
                        min = completeHoodList.get(z).getPercentage();
                    }
                }
            }
        }
        if(year == 2009){
            for(Integer z = 0; z < completeHoodList.size(); z ++){
                if(completeHoodList.get(z).getYear() == 2009){
                    if(completeHoodList.get(z).getPercentage() < min){
                        min = completeHoodList.get(z).getPercentage();
                    }
                }
            }
        }
        if(year == 2011){
            for(Integer z = 0; z < completeHoodList.size(); z ++){
                if(completeHoodList.get(z).getYear() == 2011){
                    if(completeHoodList.get(z).getPercentage() < min){
                        min = completeHoodList.get(z).getPercentage();
                    }
                }
            }
        }
    }
    public Double calculateAvg(Integer year){
        Double avg = null;
        Double sum = 0.0;
        Integer counter = 0;
        if(year == 2006){
            for(Integer z = 0; z < completeHoodList.size(); z++){
                if(completeHoodList.get(z).getYear() == 2006){
                    sum = sum + completeHoodList.get(z).getPercentage();
                    counter = counter + 1;
                }
            }
        }
        return Math.round((sum/counter) * Math.pow(10, 1)) / Math.pow(10, 1);

    }
    @Override
    public void onNothingSelected(AdapterView<?> parent) {

    }
    public void refreshFragment(){
        //refreshes the Fragment
        hoodDataList.clear();
        FragmentTransaction transaction = getFragmentManager().beginTransaction();
        transaction.detach(this).attach(this).commit();
    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        final View view = inflater.inflate(R.layout.fragment_graph,
                container, false);
        //API Request for all the hoods
        getAllData();
        getDataFromApi((GraphView) view.findViewById(R.id.graph));
        getDataForSpinner((Spinner) view.findViewById(R.id.spinner));
        return view;
    }

    public void setHoodId(Integer hood){
        hoodSelector = hood;
    }

    public void getAllData(){
        RequestQueue rq = Volley.newRequestQueue(getActivity().getApplicationContext());
        String url= "http://test.dontstealmywag.ga/api/theft_outof_car_wijk.php";
        StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        // Do something with the response
                        try{
                            JSONObject o = new JSONObject(response);
                            JSONArray values=o.getJSONArray("");
                            for (int i = 0; i < values.length(); i++) {
                                JSONObject jsonObject = values.getJSONObject(i);
                                completeHoodList.add(new HoodData(jsonObject.getDouble("percentage"), jsonObject.getInt("hood_id"), jsonObject.getInt("year"), jsonObject.getString("hood_name")));
                            }

                        }  catch (JSONException ex){}

                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        // Handle error
                    }
                });


        rq.add(stringRequest);
    }

    public void getDataFromApi(final GraphView graph) {
        RequestQueue rq = Volley.newRequestQueue(getActivity().getApplicationContext());
        String url= "http://test.dontstealmywag.ga/api/theft_outof_car_wijk.php?hood_id=" + hoodSelector;
        StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        // Do something with the response
                        try{
                            JSONObject o = new JSONObject(response);
                            JSONArray values=o.getJSONArray("");
                            for (int i = 0; i < values.length(); i++) {
                                JSONObject jsonObject = values.getJSONObject(i);
                                hoodDataList.add(new HoodData(jsonObject.getDouble("percentage"), jsonObject.getInt("hood_id"), jsonObject.getInt("year"), jsonObject.getString("hood_name")));
                            }

                        }  catch (JSONException ex){}
                        StaticLabelsFormatter staticLabelsFormatter = new StaticLabelsFormatter(graph);
                        LineGraphSeries<DataPoint> series = new LineGraphSeries<>(new DataPoint[] {
                                new DataPoint(1, (calculateAvg(2006 /2))),
                                new DataPoint(2, hoodDataList.get(1).getPercentage()),
                                new DataPoint(3, hoodDataList.get(2).getPercentage()),
                                new DataPoint(4, hoodDataList.get(3).getPercentage()),
                                new DataPoint(5, hoodDataList.get(4).getPercentage())
                                //new DataPoint(12, 0)
                        });
                        LineGraphSeries<DataPoint> average = new LineGraphSeries<>(new DataPoint[]{
                                new DataPoint(1, 16.2),
                                new DataPoint(2, 15.5),
                                new DataPoint(3, 15.2),
                                new DataPoint(4, 15.9),
                                new DataPoint(5, 13.9)
                        });

                        // set manual x bounds
                        staticLabelsFormatter.setHorizontalLabels(new String[] {"2006", "2007","2008","2009","2011"});
                        //creates custom x-axis
                        graph.getGridLabelRenderer().setLabelFormatter(staticLabelsFormatter);
                        graph.setTitle("Wijk " + hoodSelector + " - " + hoodDataList.get(0).getHood_name());
                        //set nice background color :)
                        series.setDrawBackground(true);
                        //shows points at datapoints
                        series.setDrawDataPoints(true);
                        average.setDrawDataPoints(true);
                        //size of the points
                        series.setDataPointsRadius(10.0f);
                        series.setOnDataPointTapListener(new OnDataPointTapListener() {
                            @Override
                            public void onTap(Series series, DataPointInterface dataPoint) {
                                Toast.makeText(getActivity(), "Punt "+ dataPoint, Toast.LENGTH_SHORT).show();
                            }
                        });
                        series.setTitle("%");
                        series.setAnimated(true);
                        average.setAnimated(true);
                        average.setColor(Color.argb(255, 0, 51, 153));
                        average.setThickness(5);
                        series.setColor(Color.argb(255, 102, 204, 255));
                        graph.addSeries(average);
                        graph.getLegendRenderer().setVisible(true);
                        graph.getLegendRenderer().setAlign(LegendRenderer.LegendAlign.TOP);
                        graph.addSeries(series);




                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        // Handle error
                    }
                });


        rq.add(stringRequest);
    }
    public void getDataForSpinner(final Spinner spinner){
        RequestQueue rq = Volley.newRequestQueue(getActivity().getApplicationContext());
        String url= "http://test.dontstealmywag.ga/api/theft_outof_car_wijk.php";
        StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        // Do something with the response

                        try{
                            JSONObject o = new JSONObject(response);
                            JSONArray values=o.getJSONArray("");
                            for (int i = 0; i < values.length(); i++) {
                                JSONObject jsonObject = values.getJSONObject(i);
                                if (!hoodList.contains(jsonObject.getString("hood_name"))) {
                                    hoodList.add(jsonObject.getString("hood_name"));
                                }
                            }
                        }  catch (JSONException ex){}

                        ArrayAdapter<String> adapter = new ArrayAdapter<String>(spinner.getContext(), android.R.layout.simple_spinner_item, hoodList);
                        // Specify the layout to use when the list of choices appears
                        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                        // Apply the adapter to the spinner
                        spinner.setPrompt("Title");
                        spinner.setAdapter(adapter);

                        spinner.setOnItemSelectedListener(GraphFrameV2.this);


                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        // Handle error
                    }
                });


        rq.add(stringRequest);
    }


}

The problem:

I've written this code. When I call calculateMax(2006) inside getAllData it works fine and gives me the toast I want but when I call it inside getDataFromApi the app crashed telling me that my list doesn't contain any items.

It's very weird because my calculateAvg() method does work.

Could anyone help me fix this?

Did you notice that all the code inside your ifs are exactly the same? — GVillani82
– GVillani82, Commented Apr 19, 2017 at 18:25
@GVillani82 Yeah but I don't know how to do this another way — Sander bakker
– Sander bakker, Commented Apr 19, 2017 at 18:26
You added an example that works: you should provide the one that doesn't work and add the stacktrace — GVillani82
– GVillani82, Commented Apr 19, 2017 at 18:35

GVillani82 · Accepted Answer · 2017-04-19 18:42:42Z

1

The problem is related to the fact that a network request is async by nature.

Supposing to have 3 synchronous actions (A, B, C)

Start A
Complete A
Start B
Complete B
Start C
Complete C

If B is asynchronous it can happen that

Start A
Complete A
Start B (async)
Start C (maybe C need the result from B, but unfortunately B is still running, on another thread)
Complete C
Complete B

So, you basically have to wait until the Async operation completes if your next action needs a result from it.

In order to do it, you need your next action to be executed in the callback onResponse(). Only here the data are available.

answered Apr 19, 2017 at 18:42

GVillani82

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Comments

cyroxis · Accepted Answer · 2017-04-19 18:48:54Z

Can greatly simplify your calculateMin & calcualteMax methods by setting using completeHoodList.get(z).getYear() == year

Example:

public Double calculateMin(Integer year){
    Double min = Intenger.MAX_VALUE; // Or whatever default value if the list is size 0
    for(Integer z = 0; z < completeHoodList.size(); z ++){
        if(completeHoodList.get(z).getYear() == year){
            if(completeHoodList.get(z).getPercentage() < min){
                min = completeHoodList.get(z).getPercentage();
            }
        }
   }
   return min;
}

You can even take that one step further by using a for-each loop instead of a for loop.

Example:

public Double calculateMin(Integer year){
    Double min = Intenger.MAX_VALUE; // Or whatever default value if the list is size 0
    for(HoodData hoodData : completeHoodList){
        if(hoodData.getYear() == year){
            if(hoodData.getPercentage() < min){
                min = hoodData.getPercentage();
            }
        }
   }
   return min;
}

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