public class MySQLiteHelper extends SQLiteOpenHelper{
    final static String DB_NAME = "citiesdata.db";
    final static String TABLE_NAME = "allcities";
    final static String ID = "_id";
    final static String CITY_CODE = "city_code";
    final static int DB_VERSION = 1;
    private SQLiteDatabase db;
    Context cont;

    public MySQLiteHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
        cont = context;
        Toast.makeText(cont, "constructor called", Toast.LENGTH_LONG).show();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        Toast.makeText(cont, "onCreate method called", Toast.LENGTH_LONG).show();
        String createTable = "CREATE TABLE IF NOT EXISTS " + TABLE_NAME + "(" + ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + CITY_CODE + " TEXT);";
        db.execSQL(createTable);

//      INSERTING RECORDS IN DATABASE
        SQLiteDatabase writableDB = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(CITY_CODE, "333");
        writableDB.insert(TABLE_NAME, null, values);
        writableDB.close();
        readCity();
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Toast.makeText(cont, "onUpgrade method called", Toast.LENGTH_LONG).show();
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }


    public void readCity(){
        Toast.makeText(cont, "readCity method called", Toast.LENGTH_LONG).show();
        String selectQuery = "SELECT  * FROM " + TABLE_NAME;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);
        Toast.makeText(cont, cursor.getString(cursor.getColumnIndex(CITY_CODE)), Toast.LENGTH_LONG).show();
        db.close();
    }
}

new MySQLiteHelper(MainActivity.this);

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_INTERNAL_STORAGE"/>

public void fillTable(){
    db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(CITY_CODE, "333");
    db.insert(TABLE_NAME, null, values);
    db.close();
    readCity();
}

new MySQLiteHelper(MainActivity.this).fillTable();

public MySQLiteHelper(Context context) {
    super(context, DB_NAME, null, DB_VERSION);
    cont = context;
    SQLiteDatabase db = this.getReadableDatabase();
    Toast.makeText(cont, "constructor called", Toast.LENGTH_LONG).show();
}