Concentration/Matching Game

Question

My final project for my Java class is to make a card game. I chose matching (concentration). I've got the basic code almost finished except that I got stuck when trying to add an ActionListener to each card in the deck. The method called by the ActionListener needs to modify the card object when it is called, but I don't know how to make the reference for it. I've tried global variables, but BlueJ tells me that it can't use a reference from an inner class or something. Here's my code for the user interface (which also handles the shuffling and such):
* This is the user interface for the Matching game.
* This class also handles the variable number of cards to generate.
* ArrayList will be used to manage the cards within this class.
* @author Maarten deVriend
* @version May 28, 2008
import java.awt.*;
import javax.swing.*;
import java.awt.Toolkit;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Random;
public class MatchingUI
    private JFrame frame;
    private JInternalFrame cardFrame;
    private JInternalFrame menuFrame;
    private ArrayList<Card> cards;
    private MatchingEngine engine;
     * Creates a user interface with cards, a New Game button, and a Quit button
     * The user may specify how many cards he/she would like to choose from.
    public MatchingUI(int row, int column)
        createFrame(row,column);
        engine = new MatchingEngine();
     * Creates the frame and buttons. The user may specify how many rows and
     * columns of cards to add to the grid.
     * The number of rows and number of columns cannot both be odd
    public void createFrame(int row, int column)
        cardFrame = new JInternalFrame("");
        Container cardContentPane = cardFrame.getContentPane();
            //Statement below ensures that the number of cards is even and positive.
            //There is NO check for rediculously large numbers.
            //Please be reasonable.
            if(row<=0 || column <=0)
                //Set defaults.
                cardContentPane.setLayout(new GridLayout(4,4));
                makeCards(4,4);
                Collections.shuffle(cards, new Random());
                for(Card card : cards)
                    card.addActionListener(new ActionListener()
                        public void actionPerformed(ActionEvent e)
                            cardListener();
                    cardContentPane.add(card);
                System.out.println("Negative numbers are not allowed. Setting defaults...");
            else if(row%2==1 && column%2==1)
                //Adjust row because odd multiplied by odd is always odd.
                cardContentPane.setLayout(new GridLayout(row+1,column));
                makeCards(row+1,column);
                Collections.shuffle(cards, new Random());               
                for(Card card : cards)
                    card.addActionListener(new ActionListener()
                        public void actionPerformed(ActionEvent e)
                            cardListener();
                    cardContentPane.add(card);
            else
                //The numbers are acceptable! There's hope afterall.
                cardContentPane.setLayout(new GridLayout(row,column));
                makeCards(row,column);
                Collections.shuffle(cards, new Random());
                //Add an ActionListener to each card in the deck.               
                for(Card card : cards)
                    card.addActionListener(new ActionListener()
                        public void actionPerformed(ActionEvent e)
                            cardListener();
                    cardContentPane.add(card);
        menuFrame = new JInternalFrame("");
        Container menuContentPane = menuFrame.getContentPane();
        JMenuBar menubar = new JMenuBar();
            JMenuItem newGame = new JMenuItem("New Game");
            menubar.add(newGame);
            JMenuItem quit = new JMenuItem("Quit");
            menubar.add(quit);
        menuContentPane.add(menubar, BorderLayout.NORTH);
        frame = new JFrame("Matching v1.0");
        Container contentPane = frame.getContentPane();
        contentPane.setLayout(new BorderLayout());
        contentPane.add(cardContentPane, BorderLayout.CENTER);
        contentPane.add(menuContentPane, BorderLayout.NORTH);
        frame.pack();
        frame.setVisible(true);
     * The iterator should be safe since the number is adjusted
     * in createFrame if it is negative. The compiler will give
     * an error, however.
     * Card extends JButton and has a couple extra reference fields.
    public void makeCards(int row, int column)
        //Sets up the ArrayList of Cards
        cards = new ArrayList<Card>();
        for(int i=0; i<(row*column); i++)
            Card c = new Card();
            c.setIndex(i%4);
            c.setCardIcon(new ImageIcon("card"+(i%4)+".jpg"));
            c.setIcon(new ImageIcon("cardDefault.jpg"));
            cards.add(c);
    public void cardListener()
        if(engine.getFirstCard().getFace()==false &&
        engine.getSecondCard().getFace()==false)
        //Both cards are face down. Flip the chosen card.                           
            //This is where I'm having problems.
            card.setFace(true);
            card.setIcon(getCardIcon());
            engine.setFirstCard(card);
        else
        //The first card is face up. Flip the second one and compare them.
            card.setFace(true);
            card.setIcon(getCardIcon());
            engine.setSecondCard(card);
            engine.compare();
}The MatchingEngine class handles the actual comparison of the two selected cards:
* MatchingEngine handles the process of matching the selected cards and
* eliminating them from the grid. For the most part, it contains methods
* that can be used by other classes (the MatchingUI in particular).
* @author Maarten deVriend
* @version June 3, 2008
public class MatchingEngine
    private Card firstCard;
    private Card secondCard;
    public MatchingEngine()
        //Empty, for the time being.
    public void setFirstCard(Card card)
        firstCard = card;
    public void setSecondCard(Card card)
        secondCard = card;
    public Card getFirstCard()
        return firstCard;
    public Card getSecondCard()
        return secondCard;
    public void compare()
        if((firstCard).equals(secondCard))
            //Remove the clickability of the cards.
            firstCard.setMatched();
            secondCard.setMatched();
        else
            //Flip the cards so they are face down again
            firstCard.setDefaultImage();
            secondCard.setDefaultImage();
}And finally, here is the Card class. It's a subclass of JButton with some extra flags added for the game:
* Write a description of class Card here.
* @author (your name)
* @version (a version number or a date)
import java.awt.*;
import javax.swing.*;
import java.awt.Toolkit;
import java.awt.event.*;
public class Card extends JButton
    int index;
    boolean isFaceUp;
    boolean matched;
    ImageIcon faceUp;
    public Card()
        super();
        index = 0;
        isFaceUp = false;
        matched = false;
        faceUp = new ImageIcon();
     * The following methods allow the other classes to minipulate
     * the fields in an individual Card
    public void setIndex(int i)
        index = i;
    public int getIndex()
        return index;
    public void isFaceUp()
        isFaceUp = true;
    public void isFaceDown()
        isFaceUp = false;
    public boolean getFace()
        return isFaceUp;
    public void setCardIcon(ImageIcon icon)
        faceUp = icon;
    public ImageIcon getCardIcon()
        return faceUp;
    public void setMatched()
        matched = true;
        setIcon(new ImageIcon("cardMatched.jpg"));
    public boolean getMatched()
        return matched;
    public void setDefaultImage()
        setIcon(new ImageIcon("cardDefault.jpg"));
}Any help I could get would be great. The main problem is resolving the reference to the individual card that is being modified by the ActionListener.

Answer 1

A couple other thoughts:
1) Do you need to override the equals( ) method in the Card class? It would seem like you do, that you would want to compare indexes or icons or something of that sort.
2) Your firstCard and secondCard will be initially set to null, and you must check for that in the button's actionlistener. This isn't a bad thing and can be used to test the current state of the program: has a firstCard been set yet or not. If no firstCard, then set it to the card pressed, and likewise if firstCard is not null but secondCard is null, then set the secondCard and compare them. If you use this, then your compare method should set the engine's first and second cards back to null after comparison.
3) You may wish to use some sort of delay mechanism when the cards don't match to give the user time enough to memorize what is held by both cards. Two possible ways to do this include to show a JOptionPane stating that there was no match. Then the two cards can be shown until the user clicks the option pane's OK button. Another way is to use a Swing Timer. If you opt for this, you'll have to temporarily inactivate your program's response to clicking while the two cards are shown.
4) Do you need to test somewhere for game over?