問題記錄（未解決）——RecyclerView適配器中的泛型指定

學習了ListView控件之後，接着開始了RecyclerView控件的探索，在學習得過程中發現了些不理解的問題，貼出代碼和問題做些記錄。

• 這是RecyclerView的適配器部分
• 沒有貼出的部分有Brother類（定義了照片和姓名）
• 主佈局和子項佈局
• 主方法

public class BrotherAdapter extends RecyclerView.Adapter<BrotherAdapter.ViewHolder> {
    private List<Brother> mBrotherList;
    
    static class ViewHolder extends RecyclerView.ViewHolder {
        ImageView brotherPicture;
        TextView brotherDescription;

        public ViewHolder(View view) {
            super(view);
            brotherPicture = (ImageView)view.findViewById(R.id.brother_picture);
            brotherDescription = (TextView)view.findViewById(R.id.brother_description);
        }
    }

    public BrotherAdapter(List<Brother> brotherList) {
        mBrotherList = brotherList;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        //返回的類型爲RecyclerView.ViewHolder和爲ViewHolder有什麼不同?
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.brother_item,parent,false);
        ViewHolder holder = new ViewHolder(view);
        return holder;
    }

    public void onBindViewHolder(ViewHolder holder, int position) {
        Brother brother = mBrotherList.get(position);
        holder.brotherPicture .setImageResource(brother.getImageId());
        holder.brotherDescription.setText(brother.getName());
    }

    @Override
    public int getItemCount() {
        return mBrotherList.size();
    }
}

問題：適配器繼承的RecyclerView.Adapter的泛型爲什麼要指定成BrotherAdapter.ViewHolder，而不像LIstView中的適配器泛型一樣直接用Brother？