database-initialization.java

    public abstract TodoDao todoDao();

    //Create the WordRoomDatabase as a singleton to prevent having multiple instances of the database opened
    //at the same time, which would be a bad thing
    private static TodoDatabase INSTANCE;
    public static final String DATABASE_NAME = "TASK_DATABASE";

    // singlton: to make sure there is no more than one copy
    // @synchronized one thread only can deal with this database
    public static synchronized TodoDatabase getInstance(Context context) {
        if(INSTANCE == null) {
            INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
                    TodoDatabase.class, DATABASE_NAME)
                    .fallbackToDestructiveMigration()
                    .build();
        }
        
        return INSTANCE;
    }