Retain & restore recycler view scroll position

StatefulRecyclerView.java

package eu.f3rog.ui.custom;

import android.content.Context;
import android.os.Bundle;
import android.os.Parcelable;
import android.support.annotation.Nullable;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;

/**
 * Class {@link StatefulRecyclerView} extends {@link RecyclerView} and adds position management on configuration changes.
 *
 * @author FrantisekGazo
 * @version 2016-03-15
 */
public final class StatefulRecyclerView
        extends RecyclerView {

    private static final String SAVED_SUPER_STATE = "super-state";
    private static final String SAVED_LAYOUT_MANAGER = "layout-manager-state";

    private Parcelable mLayoutManagerSavedState;

    public StatefulRecyclerView(Context context) {
        super(context);
    }

    public StatefulRecyclerView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public StatefulRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    protected Parcelable onSaveInstanceState() {
        Bundle bundle = new Bundle();
        bundle.putParcelable(SAVED_SUPER_STATE, super.onSaveInstanceState());
        bundle.putParcelable(SAVED_LAYOUT_MANAGER, this.getLayoutManager().onSaveInstanceState());
        return bundle;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        if (state instanceof Bundle) {
            Bundle bundle = (Bundle) state;
            mLayoutManagerSavedState = bundle.getParcelable(SAVED_LAYOUT_MANAGER);
            state = bundle.getParcelable(SAVED_SUPER_STATE);
        }
        super.onRestoreInstanceState(state);
    }

    /**
     * Restores scroll position after configuration change.
     * <p>
     * <b>NOTE:</b> Must be called after adapter has been set.
     */
    private void restorePosition() {
        if (mLayoutManagerSavedState != null) {
            this.getLayoutManager().onRestoreInstanceState(mLayoutManagerSavedState);
            mLayoutManagerSavedState = null;
        }
    }

    @Override
    public void setAdapter(Adapter adapter) {
        super.setAdapter(adapter);
        restorePosition();
    }
}

How to use this code?
Please explain a full person or send an example

Thank you for the code, this works inside fragment 👍 , but not working inside activity 👎
How to use this code?
Please explain a full person or send an example

Worked fine. Thanks

If you are looking for a solution, don't do like that, you will never know how to use the code.

Now do like this:
All below code you put in the activity (where you using the Recyclerview)

// save position:
RecyclerView rcv = findViewById(.....);
rcv.setAdapter(....);
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
rcv.setLayoutManager(layoutManager);

rcv.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                pos = layoutManager.findFirstVisibleItemPosition();
               // everytime you scroll the list, new position will be saved in app's data storage:
                SharedPreferences preferences = getSharedPreferences("anyname", MODE_PRIVATE);
                SharedPreferences.Editor editor = preferences.edit();
                editor.putInt("KEY_LAST_POSITION", pos).apply();
            }
        });

// using position: 
SharedPreferences preferences = getSharedPreferences("anyname", MODE_PRIVATE);
int position = preferences.getInt("KEY_LAST_POSITION", 0); // 0 is the default value
rcv.scrollToPosition(position);

@chieuancucbo you don't know your code. It is remembering an item position, not the exact scroll.