CompleteAdapter

public class AutoCompleteCountryAdapter extends ArrayAdapter<Countries.CountriesData> {

    private List<Countries.CountriesData> countryListFull;

    public void setCountryListFull(List<Countries.CountriesData> countryListFull) {
        this.countryListFull = countryListFull;
    }

    public AutoCompleteCountryAdapter(@NonNull Context context, @NonNull List<Countries.CountriesData> countryList) {
        super(context, 0, countryList);
        countryListFull = new ArrayList<>(countryList);
        notifyDataSetChanged();
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.country_autocomplete_row, parent, false);
        }

         TextView textViewName = convertView.findViewById(R.id.text_view_name);
         Countries.CountriesData countryItem = getItem(position);

        if (countryItem != null) {
            textViewName.setText(countryItem.getName());
        }
        return convertView;
    }

    @NonNull
    @Override
    public Filter getFilter(){
        return countryFilter;
    }

    private Filter countryFilter = new Filter() {
        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
            FilterResults results = new FilterResults();

            List<Countries.CountriesData> suggestions = new ArrayList<>();
            if (constraint == null || constraint.length() == 0) {
                suggestions.addAll(countryListFull);
            } else {

                String filterPattern = constraint.toString().toLowerCase().trim();

                for (Countries.CountriesData item : countryListFull) {
                    if (item.getName().toLowerCase().contains(filterPattern)) {
                        suggestions.add(item);
                    }
                }
            }

            results.values = suggestions;
            results.count = suggestions.size();
            return results;
        }

        @Override
        protected void publishResults(CharSequence constraint, FilterResults results) {
            clear();
            addAll((List) results.values);
            notifyDataSetChanged();
        }

        @Override
        public CharSequence convertResultToString(Object resultValue) {
            return ((Countries.CountriesData) resultValue).getName();
        }
    };
}