一、为什么要使用密闭类为了避免满足编译器的要求而写无用条件分支的情况可以使用密闭类。二、怎么使用密闭类代码如下packagecom.example.mychatimportandroid.view.Viewimportandroid.widget.TextViewimportandroidx.recyclerview.widget.RecyclerViewsealedclassMsgViewHolder(view:View):RecyclerView.ViewHolder(view)classLeftViewHolder(view:View):MsgViewHolder(view){valtvLeftMsg:TextViewview.findViewById(R.id.leftMsg)}classRightViewHolder(view:View):MsgViewHolder(view){valtvRightMsg:TextViewview.findViewById(R.id.msgRight)}去掉when后边的else分支overridefunonBindViewHolder(holder:RecyclerView.ViewHolder,position:Int){valmsgmsgList[position]Log.e(ysy,${msg.content}(holderisLeftViewHolder))when(holder){isLeftViewHolder-holder.tvLeftMsg.textmsg.contentisRightViewHolder-holder.tvRightMsg.textmsg.content}}