Re: Design decision for a game

"Peter Duniho" <>
Thu, 22 May 2008 14:17:16 -0700
On Thu, 22 May 2008 13:28:37 -0700, pek <> wrote:

OK.. I think I understand some things here. I won't be fancy, so
threshold is a little overkill (although I did like the idea). What I
see problematic here is this:
class House {
  public void addCard(Card card) {
    // do some things, or probably nothing because the rules would
take care of it
    // inform listeners
    for (HouseListener lstnr : listeners) {
      lstnr.cardAdded(this, card);

That part seems fine, as far as it goes.

class SixCardsRule implements HouseListener {
  public void cardAdded(House house, Card card) {
    if ( house.getCards().size() == 5 ) {
      // then adding this card satisfies this Rule. So,
      house.setCards(new ArrayList<Card>());
      // Now notify everyone. The 50 is for the score to be added
      for (RuleListener lstnrs : listeners) {
        lstnrs.ruleSatisfied("Six cards in total",50);

This part I'm not so sure of.

Without seeing your whole architecture, it's hard to say for sure. But =
it =

seems to me that someone other than the Rule should be maintaining the =

score. I'm not sure if this is the House, or if you have some other cla=
ss =

that's the entire Game. But it seems to me that the Rule should not =

necessarily be raising score-change events itself, but rather should be =

calling some method somewhere that adds 50 points to the score. Objects=

that need to be notified of score changes would be attached as a listene=
r =

to _that_ object.

Now, if you _also_ want to provide for notification of when a specific =

rule is satisfied, your Rules could allow those listeners to be added. =

And they would be notified much as you show above. Except that the scor=
e =

would not necessarily be part of the method parameters, at least not in =
my =


Alternatively, if you _do_ want the Rule notifications to include the =

score, then either _all_ rule-satisfying conditions should affect the =

score, or you need to expand your RuleListener interface so that there a=
re =

different methods, some of which include a point total to be added to th=
e =

score, and others that don't. Or perhaps you provide just one method in=

the interface that is the "score changed" notification", and that's sent=

separately from other notifications, like "rule satisfied".

Any of these could work. Which is "best" is hard to say. For my tastes=
, =

I'd prefer either the first suggestion or the last. If you intend for =

there only to ever be a single scoring object, then the first might be =

more appropriate. Then each Rule would have to know which object was th=
at =

single scoring object and would directly call a method on that object to=

update the score.

On the other hand, if you want your design to be more flexible, such tha=
t =

you can have multiple scorers present, then it probably makes more sense=

for the Rules to use the RuleListener interface to report score changes.=

Each scoring object can then subscribe as appropriate to the rules =

relevant for that scoring object.

As an example of this, consider something like (following your previous =

listener interface may want to consider instead following =

the usual Java model, where an "Event" class is defined that includes al=
l =

of the relevant data, including the source and the specifics of the even=

     public interface RuleListener
         void ruleSatisfied(Rule sender, string ruleName);
         void scoreChange(Rule sender, int points);

Then scoring objects can subscribe to the Rules as needed, and the UI an=
d =

other interested objects can also subscribe. If it turns out that there=
's =

little or no overlap between these two types of subscribers, you might =

even break the interface into two, with one interface dedicated to thing=
s =

that are just "activity notification" sorts of things, and the other =

dedicated to things that actually change the game state. Often one even=
t =

 from each might be raised, but only objects of the appropriate =

functionality would subscribe to the specific listener group. That way =

you don't waste a lot of time having, for example, having UI objects =

receiving and ignoring notifications for game state changes, and having =

game state objects receiving and ignoring notifications for UI events.

I think ultimately I'd go with _some_ variation on this last approach =

(that is, the one where the Rule supports listeners for events separated=

into appropriate categories, whether in the same interface or in two or =

more), but any of the above would probably work (including what you =

posted, if you really want to do it that way).

By the way, I'm not sure that the House should expose the collection =

implementation. That is, rather than a "setCards" method that takes the=

actual collection, it probably makes more sense to have a "clearCards" =

method that resets the internal implementaton. If you really need a way=

to add or set multiple cards at once from a non-empty collection, you =

could still have a more general-purpose method that takes a List<Card> =

instead of some specific collection type.


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