Javafx - Syncronization delay - card flips

Question

I'm actually working on a memory game and I'm stuck at the point where I should write the gameplay-part of the game. So: I have an array of N card objects. Each object has an attribute called cardNum - an identifier. I think I should write an actionListener on that array, so when I flip a card, it puts the flipped card's cardNum in an array of two elements and if the two elements of the array are equal, a pair is found. The problem is that I just don't know how to get the last flipped card's cardNum. Any help would be appreciated.

Here's the way I tried:

private void easyGame(Card[] cards) {
    int flippedCards = 0;
    int card1;

    while(flippedCards != 24) {
        for(int i=0; i<cards.length; i++) {
            if(cards[i].getIsFlipped())
                flippedCards ++;
        }
        if(flippedCards % 2 == 0 && flippedCards > 0)
            for(int i=0; i<cards.length; i++) {
                card1 = getCardIndByCardNum(cards[i].getCardNum(), cards, i);

                if(!cards[card1].getIsFlipped()) {
                    for(int j=0; j<cards.length; j++) {
                        if(cards[i].getIsFlipped())
                            cards[i].flip();
                    }
                    flippedCards = 0;
                    break;
                }
            }
    }
}

The problem is that if I call this method, the game won't be drawn. May I use use threads somehow?

EDIT

Here is how I get the indexes of the clicked cards, and I call it in the UI:

private void setCardHandlers() {
    for(final Card card : cards) {

        card.setOnMouseClicked(new EventHandler<MouseEvent>() {

            @Override
            public void handle(MouseEvent t) {
                clickedCardInd = getChildren().indexOf(card)-1;
            }
        });
    }
}

Than here is how I am using it:

setOnMouseReleased(new EventHandler<MouseEvent> () {

        @Override
        public void handle(MouseEvent t) {
            int cardIndex = clickedCardInd; // get index of what user clicked
            clickedCardInd = -1;
            if (cardIndex != -1 && moveRequestedFlag) { // our controller waits for the move
                // get the position and report
                moveRequestedFlag = false; // we handled the move
                //System.out.println(cardIndex);
                nextMove.setMove(cardIndex); // this will unblock controller's thread
            }
        }

    });

It has a delay on fliping cards, also in the easyGame the requestMove method sets both indexes to the same.

Answer 1

I would recommend splitting you responsibilities a bit into Model/View/Controller modules, which, in simplest case would look like :

• Model - your game current state and data, i.e. cards array Cards mCards = new Cards[24];
• View - your UI, that can reflect current state of mCards(model) on screen in Main thread
• Controller - your main game logic. This is most complex part, responsible for
  
  1. requesting/handling user move,
  2. updating mCards(model) based on user move,
  3. Requesting UI to re-draw.
     

Contoroller's code (easyGame method) should run on separate thread to not block the UI.

Below I sketched a skeleton code that should fit your requirements :

class Game {

    /*
     * controller - main logic
     */
    void startEasyGame() {
        // initialize cards array, shuffle if needed

        // we start with zero cards flipped
        int flippedCards = 0;

        // main loop
        while (flippedCards != mCards.length) {
            // 1. show updated UI
            mBoard.showUpdatedCards();

            // 2. request player move 
            // and block current thread to wait till move is done
            // the result of the move - index of the card
            int index1 = requestMove();
            // temporarily flip first card face-up
            mCards[index1].flip();
            // show it on screen
            mBoard.showUpdatedCards();

            // same for second card
            int index2 = requestMove();
            mCards[index2].flip();
            mBoard.showUpdatedCards();


            // 3. check the result
            if (mCards[index1].getCardNum() == mCards[index2].getCardNum()) {
                // hooray, correct guess, update count
                // possibly show some encouraging feedback to user
                flippedCards += 2;
            } else {
                // incorrect, flip cards back face down
                mCards[index1].flip();
                mCards[index2].flip();
            }

        } // end of while loop

        // game ended -> show score and time
        mBoard.showResult();    
    }

}

EDIT
Extra details on how to await for result from UI thread :

int requestMove() {
    // 1. show user prompt to make a move
    // ...

    // 2. construct latch to wait for move done on UI thread
    mBoard.moveRequestedFlag = true;
    NextMove nextMove = new NextMove();
    mBoard.nextMove = nextMove;

    // 3. await for move and get the result
    return nextMove.getMove();
}

then, somewhere in UI code :

// handling card onClick somewhere on UI thread
if (mBoard.moveRequestedFlag) { // our controller waits for the move
    // get the position and report
    int cardIndex = ... // get index of what user clicked
    mBoard.moveReqestedFlag = false; // we handled the move
    mBoard.nextMove.setMove(cardIndex); // this will unblock controller's thread
}

and NextMove utility class to sync threads :

public class NextMove {
    private volatile int mCardIndex;
    private final CountDownLatch mMoveReady = new CountDownLatch(1);

    public int getMove() throws InterruptedException {
        mMoveReady.await();
        return mCardIndex;
    }

    public synchronized void setMove(int selectedCardIndex) {
        if (mMoveReady.getCount() > 0) {
            mCardIndex = selectedCardIndex;
            mMoveReady.countDown();
        }
    }
}