Question

When I call this constructor to parse some JSON I’m getting a nullpointer exception when trying to insert the values into uriMap. I thought Android / Java would automatically initialize any class fields. Also when I debug the app the value of the uriMap is showing as null. I don’t see any way to initialize the map before I start using it. What am I doing wrong?

public class ServiceLocator {
    private static final String TAG = ServiceLocator.class.getSimpleName();
    Map <String,Uri>uriMap; 

    public ServiceLocator(JSONObject json){
    try {
        json = (JSONObject) new JSONTokener(testJson).nextValue();
        JSONArray locations = json.getJSONArray("data");
        int len = locations.length();
        for(int i=0; i<len; i++){
            JSONObject obj = locations.getJSONObject(4);
            String name = obj.getString("name");
            Uri uri = Uri.parse(obj.getString("url"));
            if(name != null && uri != null){
                uriMap.put(name, uri);
            }
            Log.d(TAG, "Inserted key(" + name + "),value(" + uri.toString() + ") into tempMap");
        }
    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (NullPointerException e){
        Log.d(TAG, "Error inserting into map", e);
    }
    }
}

Answer 1

You have to initialize the map yourself.

Map <String,Uri> uriMap = new HashMap <String,Uri>();