Android SQLite Getting always true when checking if the result exits

Im making a login and register system and if need to check if the user already exits so I wrote this function in my database handler to check it.

public boolean checkIfUserExits(String username){
    SQLiteDatabase db = this.getWritableDatabase();
    String query = "SELECT * FROM " + TABLE_NAME + " WHERE username=" + "\"" + username + "\"";
    Cursor cursor = db.rawQuery(query, null);

    if(cursor.getCount() <= 0){
        cursor.close();
        return false;
    }
    cursor.close();
    return true;
}

But the problem if that i always getting a true. Thanks for help.