Android : Accessing json string in java and creating hashmap Android

I have a JSON string and I am trying to retrieve information from it. Json String looks like this.

{"information":{"device":{"id":0},"user":{"id":0},"data":[{"datum":{"id":"00GF001","history_id":"9992BH","name":"abc","marks":57,"class":"B","type":"Student"}},{"datum":{"id":"72BA9585","history_id":"78NAH2","name":"ndnmanet","marks":70,"class":"B","type":"Student"}},{"datum":{"id":"69AHH85","history_id":"NN00E3006","name":"kit","department":"EF003","class":"A","type":"Employee"}},{"datum":{"id":"09HL543","history_id":"34QWFTA","name":"jeff","department":"BH004","class":"A1","type":"Employee_HR"}}]}}

I am trying to access data JSONArray and respective Datum from it. I differentiated each datum as per type such as student, employee etc and push information in hashmap. I successfully did it in javascript but in Java I am struggle abit.

When I am trying to access JSONArray it throws exception

 try {
            JSONObject data = new JSONObject(dataInfo);
           // Log.d(TAG, "CHECK"+data.toString());

            if(current.getJSONArray("data").length() > 0)  //exception here

                Log.d(TAG, "Data"+ data.getJSONArray("signals").length()); //exception here too
            for(int m = 0; m < data.length(); m++){
                //   for(int s = 0; s < data[m].ge)
            }
        } catch (JSONException j){
            j.printStackTrace();
        }

Any pointers to create hashmap respective type I have. Appreciated