Why writing an Inner Private class inside <> bracket of outer class makes error?

I'm trying to insert a private class into brackets (Generics) of outer class declaration and getting the next error : "com.example.gridrecyclerview.RecyclerViewAdapter.VieHolder has private access in com.example.gridrecyclerview.RecyclerViewAdapter"

When changing inner class to public everything ok. Can someone explain me the issue.
Attached code:

    package com.example.gridrecyclerview;
import android.content.Context;
import android.graphics.Color;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.List;
import java.util.Random;
public class RecyclerViewAdapter extends RecyclerView.Adapter <RecyclerViewAdapter.ViewHolder> {
Context context;
List<ModelItem> modelItemList;
public RecyclerViewAdapter(Context context, List<ModelItem> modelItemList)
{
this.context = context;
this.modelItemList = modelItemList;
}
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType)
{
View view = LayoutInflater.from(context).inflate(R.layout.rc_item,parent,false);
return new ViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position)
{
Log.e("onBindViewHolder ","onBindViewHolder");
ModelItem modelItem = modelItemList.get(position);
holder.firstNameTextView.setText(modelItem.getFirstName());
holder.secondNameText.setText(modelItem.getLastName());
}
@Override
public int getItemCount()
{
return modelItemList.size();
}
private class ViewHolder extends RecyclerView.ViewHolder
{
TextView firstNameTextView;
TextView secondNameText;
public ViewHolder(@NonNull View itemView)
{
super(itemView);
firstNameTextView = itemView.findViewById(R.id.first_name);
secondNameText = itemView.findViewById(R.id.second_name);
}
}
}

You can not do this, because there you are passing the private class to "RecyclerView.Adapter" class. In other words, the ViewHolder class only available inside the RecyclerViewAdapter class.

PS: You can create this class as a new Class, then pass it through "RecyclerView.Adapter" class or change it to public scope.

To answer this question you should know what happened behind the scene when you use generics in Java, Generics are checked at compile time and there is no generic type at runtime this is called type erasure, when you compile your program all generics are castes to their specific types. Imagine your RecyclerView.Adapter class is something as follow:

public class Adapter<T> {
T view;
public T getView() {
return view;
}
public void setView(T view) {
this.view = view;
}
}

And Imagine you have defined your RecyclerViewAdapter class as before:

Now lets discuss this problem from two points of view:

1. Programmer
2. Compiler

As a programmer imagine somewhere in another class you create an instance of RecyclerViewAdapter class as follow and call getView() on that object:

RecyclerViewAdapter recycler = RecyclerViewAdapter();
? object =  recycler.getView()

What type of object you put here instead of ?
clearly you can't put RecyclerViewAdapter.ViewHolder because it is private for RecyclerViewAdapter and you can't use it elsewhere.

Now lets consider this problem from compiler point of view:

When compiling generics, compiler use erasure and compile your code to something like this:

RecyclerViewAdapter recycler = RecyclerViewAdapter();
? object =  (RecyclerViewAdapter.ViewHolder)recycler.getView();

Here you can see compiler cast the type of your object at compile time((RecyclerViewAdapter.ViewHolder)recycler.getView()). But is it possible for compiler to do something like this here?

Of course not because RecyclerViewAdapter.ViewHolder is private for RecyclerViewAdapter class while this code is written in another class.

As per the accessibility rule in Java-Spec Page -164, a private member declared is accessible only within the body of the top level class. I hope body of the class means not the definition of it.

**
Otherwise, the member or constructor is declared private, and access is permitted if and only if it occurs within the body of the top level class (§7.6) that encloses the declaration of the member or constructor.
**