Android Studio – Error: Member not found: 'NoteDatabaseHelper._initializeNoteDatabase'

An error showed up while I was making an note app. I feel that I code everything correct but still I this error is showing:

"Error: Member not found: ‘NoteDatabaseHelper._initializeNoteDatabase’.
final Future dbFuture = NoteDatabaseHelper._initializeNoteDatabase();"

This is my note list file.

class ScreenNote extends StatefulWidget {
  @override
  _ScreenNote createState() => _ScreenNote();
}

class _ScreenNote extends State<ScreenNote> {
  late List<Note>? noteList;
  int count = 0;

  @override
  Widget build(BuildContext context) {
    if (noteList == null) {
      noteList = <Note>[];
      updateListView();
    }

    return ClipRRect(
        child: Slidable(child: GestureDetector(child: getNoteListView())));
  }

  ListView getNoteListView() {
    return ListView.builder(
      itemCount: count,
      itemBuilder: (BuildContext context, int position) {
        return Card(
          color: Colors.white,
          elevation: 2.0,
          child: Stack(
            children: [InkWell( onTap: () {
              editnote(this.noteList![position]);
            },),
              ListTile(
                title: Text(this.noteList![position].title as String),
                subtitle: Text(this.noteList![position].date as String),
              ),],
          )
        );
      },
    );
  }

  void editnote(Note note) async {
    bool result = await Navigator.push(context, MaterialPageRoute(builder: (context) {
      return NoteEditor(note);
    }));

    if (result == true) {
      updateListView();
    }
  }

  void updateListView() {
    final Future<Database> dbFuture = NoteDatabaseHelper._initializeNoteDatabase();
    dbFuture.then((database)                                      //error is shown here 
    {
      Future<List<Map<String, dynamic>>?> noteListFuture = NoteDatabaseHelper.queryAll();
      noteListFuture.then((noteList) {
        setState(() {
          this.noteList = noteList?.cast<Note>();
          this.count = noteList?.length as int;
        });
      });
    });
  }
}

This is my database helper file

class NoteDatabaseHelper {
  static final _dbName = 'noteDatabase.db';
  static final _dbVersion = 1;
  static final _tableName = 'noteTable';

  static final columnId = '_Id';
  static final columnTitle = '_Title';
  static final columnDescription = '_Description';
  static final columnDate = '_Date';

  NoteDatabaseHelper._privateConstructor();

  static final NoteDatabaseHelper instance =
      NoteDatabaseHelper._privateConstructor();

  static Database? _notedatabase;

  Future<Database?> get notedatabase async {
    if(notedatabase!=null){
      return _notedatabase;
    }
    else{
      _notedatabase = _initializeNoteDatabase() as Database?;
      return _notedatabase;
    }
  }

  Future<Database?> _initializeNoteDatabase() async{
    Directory directory = await getApplicationDocumentsDirectory();
    String path = join(directory.path, _dbName);
    return await openDatabase(path,version: _dbVersion, onCreate: _onCreate);
  }

  Future? _onCreate(Database db, int version){
    db.query(
      '''
      CREATE TABLE $_tableName(
      $columnId INTEGER PRIMARY KEY AUTOINCREMENT, 
      $columnTitle TEXT, 
            $columnDescription TEXT, 
            $columnDate TEXT)')
      '''
    );
  }

  static Future<int?> insert(Note note) async{
    Database? db = await instance.notedatabase;
    return await db?.insert(_tableName, note.toMap());
  }

  static Future<List<Map<String, dynamic>>?> queryAll() async{
    Database? db = await instance.notedatabase;
    return await db?.query(_tableName);
  }

  static Future<int?> update(Note note) async{
    Database? db = await instance.notedatabase;
    return await db?.update(_tableName, note.toMap(), where: '$columnId = ?', whereArgs: [note.id]);
  }

  static Future<int?> delete(Note note) async{
    Database? db = await instance.notedatabase;
    return await db?.delete(_tableName, where: '$columnId = ?', whereArgs: [note.id]);
  }
}

Please I am new to flutter. Can anyone help me out?

Full preoject(not completed): https://github.com/SayanBanerjee09082002/Daily_Utility