I have a question for Android listview

@Override
        public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
            ViewHolder holder;

            if (convertView == null) {
                convertView = inf.inflate(R.layout.list_group, parent, false);

                holder = new ViewHolder();
                holder.text = (TextView) convertView.findViewById(R.id.lblListHeader);
                convertView.setTag(holder);
            } } else {
                holder = (ViewHolder) convertView.getTag();
            }
            ImageView imageView = (ImageView) convertView.findViewById(R.id.indicator);
            if(isExpanded){
                imageView.setImageResource(R.drawable.arrowup);
            } } else {
                imageView.setImageResource(R.drawable.arrowdown);
            }
            holder.text.setText(getGroup(groupPosition).toString());
             return convertView;
        }

        @Override
        public boolean isChildSelectable(int groupPosition, int childPosition) {
            return true;
        }

        private class ViewHolder {
            TextView text;
        }
    }
}

ImageView imageView = (ImageView) convertView.findViewById(R.id.indicator);
            if(isExpanded){
                imageView.setImageResource(R.drawable.arrowup);
            } } else {
                imageView.setImageResource(R.drawable.arrowdown);
            }