CustomAdapter.java

@Override 
  public void onBindViewHolder(ViewHolder holder, int position) {
      Movie movie = movies.get(position);

      holder.title.setText(movie.getTitle());  
      holder.rating.setText(movie.getRating());

      //SRP violation, onBindViewHolder has only the responsibility to display data
      // & not make data formatting operations

      String[] genres = song.getGenres();
      StringBuilder builder = new StringBuilder();
      foreach (String genre : genres){
        builder.append(genre).append(",");
      }

      holder.genres.setText(builder.toString());
  }