public void addItem(Artist artist){
  if (artist == null)   throw new NullPointerException("The item cannot be null");
  artists.add(artist);
  notifyItemInserted(getItemCount() - 1);
}

public void addItem ( Artist artist ) { if ( artist == null ) throw new NullPointerException ( "The item cannot be null" ) ; artists . add ( artist ) ; notifyItemInserted ( getItemCount ( ) - 1 ) ; }
add item in the last index
