Error in sending Arraylist to Adapter in Recycler view in Android

Question

I have an arraylist CastArrayList in which data is added in the onResponse method of Volley and from there I want to check if the size of CastArrayList is greater than 7, another arraylist subCastArrayList copies the CastArraylist from position 0 to 7 and send it to RecyclerView but not getting any view in RecyclerView . I want if CastArrayList size is greater than 7 SubCastArrayList should copy first 7 elements else copy the whole CastArrayList and then send the SubCastArrayList to adapter .

ArrayList<Cast> castArrayList;
ArrayList<Cast> subCastArrayList;
castArrayList = new ArrayList<>();
subCastArrayList = new ArrayList<>();

castDetailAdapter = new 
CastDetailAdapter(MovieView.this,castArrayList,subCastArrayList);

RecyclerView.LayoutManager mLayoutManager = new 
StaggeredGridLayoutManager(1,StaggeredGridLayoutManager.HORIZONTAL);

recycler_view.setLayoutManager(mLayoutManager);
recycler_view.setItemAnimator(new DefaultItemAnimator());
recycler_view.setAdapter(castDetailAdapter);

StringRequest stringRequest1 = new StringRequest(Request.Method.GET, url, 
    new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            int i;
            for (i=0;i<movieDetailFull.getCredits().getCast().size();i++) {
                Cast cast = new Cast();

                cast.setName(movieDetailFull.getCredits().getCast().get(i).getName());

                cast.setId(movieDetailFull.getCredits().getCast().get(i).getId());

                castArrayList.add(i,cast);
                castDetailAdapter.notifyDataSetChanged();
            }
        }

        if (castArrayList.size() > 7) {

            subCastArrayList  = new ArrayList<Cast>
            (castArrayList.subList(0,6));
            castDetailAdapter.notifyDataSetChanged();
        }
        else {
            subCastArrayList = new ArrayList<Cast>(castArrayList);
            castDetailAdapter.notifyDataSetChanged();
        }

Answer 1

You are changing the reference of subCastArrayList list by creating new arraylist mean now subCastArrayList and list in adapter are two different reference to different list

so just add elements to it

subCastArrayList.clear();
// ^^^ clear the list instead of creating new one inside if or else
if (castArrayList.size() > 7)
{
    //subCastArrayList.addAll(castArrayList.subList(0,6));
    subCastArrayList.addAll(castArrayList.subList(0,7));
    // upper range is exclusive so use              ^ 
}else{
    subCastArrayList.addAll(castArrayList);
}
    castDetailAdapter.notifyDataSetChanged();
   // move notify outside , avoid redundant statements