How to add data into a json array instead of a ArrayList?

You can do this way:

JSONArray jRootArray = new JSONArray();        for (int i = 1; i <= 20; i++) {            JSONObject jInnerObject = new JSONObject();            try {                jInnerObject.put(String.valueOf(i), "Hello "+i);            } catch (JSONException e) {                e.printStackTrace();            }            jRootArray.put(jInnerObject);        }        Log.i("JRootArray", jRootArray.toString());

Hope this will help you.

Try this:

private Map<String, String> itemselected = new HashMap<>();   private void selectedItems() {    JSONArray itemSelectedJson = new JSONArray();    // Retrieve all keys    Set<String> keys = itemselected.keySet();     // Add items to JSONArray as JSONObjects    for(String key : keys) {        itemSelectedJson.put(            new JSONObject().put(key, itemselected.get(key))        );    }}

This way, you won't have to pass by an ArrayList to fill your JSONArray. Then, you can get your JSON string simply by calling the toString() method on the JSON array:

String jsonString = itemSelectedJson.toString();