unable to save data from json array

I am trying to extract some data from a json array file, i followed the steps from Reading a Json Array in android

a snippit of the json array:

[
{
"JobNo": 1,
"JobTime": 30,
"JobDate": "20170911",
"WorkerTime": 27,
"JobTimeError": -3
},
{
"JobNo": 2,
"JobTime": 22,
"JobDate": "20170911",
"WorkerTime": 21,
"JobTimeError": -1
},

What i want to be able to do is, extract the data and store them into their own arrays, JobNo to JobNo array, etc. the following code is my attempt, but it doesn't store the values (crashes at toast because it says no data in array). thanks

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Spinner staticSpinner = (Spinner) findViewById(R.id.static_spinner);
    ArrayList<Integer> JobNo = new ArrayList<>();
    ArrayList<Integer> JobTime= new ArrayList<>();
    ArrayList<String> JobDate= new ArrayList<>();
    ArrayList<Integer> WorkerTime= new ArrayList<>();
    ArrayList<Integer> JobTimeError = new ArrayList<>();

    try {
        JSONObject json = new JSONObject(loadJSONFromAsset());
        JSONArray jArray = json.getJSONArray("Data");

        for (int i = 0; i < jArray.length(); i++) {
            JSONObject json_data = jArray.getJSONObject(i);
            int JobN = json_data.getInt("JobNo");
            int JobT = json_data.getInt("JobTime");
            String JobD = json_data.getString("JobDate");
            int WorkT = json_data.getInt("WorkerTime");
            int JobTE = json_data.getInt("JobTimeError");
            JobNo.add(JobN);
            JobTime.add(JobT);
            JobDate.add(JobD);
            WorkerTime.add(WorkT);
            JobTimeError.add(JobTE);

        }
    }
    catch (JSONException e) {
        e.printStackTrace();
    }
    Toast.makeText(this,
            JobDate.get(1),
            Toast.LENGTH_LONG).show();
}

    public String loadJSONFromAsset() {
    String json = null;
    try {

        InputStream is = getAssets().open("convertcsv.json");

        int size = is.available();

        byte[] buffer = new byte[size];

        is.read(buffer);

        is.close();

        json = new String(buffer, "UTF-8");


    } catch (IOException ex) {
        ex.printStackTrace();
        return null;
    }
    return json;

}