Need help with constructor and fields

[Richard Goodwin]

Hi there,

I am a bit stumped on a problem.

I am currently working on a solitaire game code. I need to create a class called Stock (a non graphical version). I need to implement a constructor with only a single parameter plus a few methods called top, takeTop, numCardsRemaining and toString.

At the moment my Stock class is currently empty, as I cannot work out what the fields and constructor should be.

The Javadoc for the stock class is sort of helpful. It says...
Constructor summary
Stock(Deck deck)

To develop the Stock class you need to understand the Deck class, so here is the code for the deck class.
Thanks

Deck class code

  
import java.util.*;
import java.awt.*;
 
/**
 * A full deck of cards. It is shuffled when first constructed
 * and thereafter cards are removed from the deck by calls to 
 * nextCard until no further cards remain. Cards can also be
 * placed back on the deck at either the start or the end.
 */
public class Deck
{
    private java.util.List<Card> cards;      // The list of cards
    private static java.util.Random generator = null;
    
    /**
     * Constructor for a shuffled deck of cards.
     * @param seed the seed for the random number generator used to
     * shuffle the deck. A different unique shuffle is obtained for
     * each possible value of seed.
     */
    public Deck(long seed)
    {
        // Create a deck of cards in sorted order of suit then pip count.
        
        cards = new ArrayList<Card>();
        for (int suit = Card.SPADES; suit <= Card.CLUBS; suit++) {
            for (int pips = 1; pips <= Card.CARDS_IN_SUIT; pips++) {
                cards.add(new Card(suit, pips));
            }
        }
        
        // Now shuffle the deck, using a random number generator based
        // on the seed value given as a parameter.
        
        java.util.Random generator = new java.util.Random(seed); 
        java.util.Collections.shuffle(cards, generator);
    }
     
    /**
     * The number of cards still remaining in the deck.
     * @return the number of cards left in the deck.
     */
    public int numCardsRemaining()
    {
        return cards.size();
    }
    
    /**
     * Get the next card from the deck, reducing the number of cards
     * remaining in the deck by one.
     * @return the "top" card in the deck
     */
    public Card nextCard()
    {
        return cards.remove(0);
    }
    
    /**
     * Add the given card to the start (front) of the current deck.
     * @param card the card to be placed at the start of the deck
     */
    public void addAtStart(Card card)
    {
        cards.add(0, card);
    }
    
    /**
     * Add the given card to the end (back) of the current deck.
     * @param card the card to be placed on the end of the deck
     */
    public void addAtEnd(Card card)
    {
        cards.add(card);
    }
}  

So basically, I am wondering how do I do the constructor and fields for the Stock class.

Thanks

[ May 03, 2006: Message edited by: Richard Goodwin ]

Also: is this the appropriate forum for this question? Should I have posted it in the intermediate forum instead?
[ May 03, 2006: Message edited by: Richard Goodwin ]

[Peter Brockway]

It looks like Stock only needs a single field - the Deck that is
used to construct it. All the methods you mention could be
implemented using this field.

(The Deck documentation is a little strange as this class does
not model a full deck.)

[Richard Goodwinn]

I still can't get the Stock class to work. I can't even figure out how to get the public Card takeTop() method to work.

The javadoc says

public Card takeTop()
Take the top card from the stock.
Returns:
the card that was on top of the stock or null if the stock was empty. A call to this method reduces the number of cards remaining in the stock by one.

Im sort of lost! I suspect I will need to create an array for this method, but every one Ive tried has failed to compile. Bah I suck at Java!

Help?

Thanks

[Richard Goodwinn]

THe constructor I wrote for the Stock method is this

private Deck deck;
    public Stock(Deck deck)
    {
        this.deck = deck;
    }

Is that right?

[Richard Goodwinn]

Hmm so these are the methods I need to create for the Stock class.

public void addAtEnd(Card card)
add the given card to the end of the stock of the cards

public int numCardsRemaining()
the number of cards in the stock (including the top card)
Returns: the number of cards

public Card takeTop()
take the top card from the stock
returns: the card that was on top of the stock or null if the stock was empty. A call to this method reduces the number of cards remaining in the stock by one.

public Card top()
the top card of the stock
returns: the top card of the stock, or null if the stock is empty. A call to this method does not remove the card from the top but just returns a reference to it.

public String toString
String representation of a Stock object
returns: a string representing the Stock. THe string consists of the String representation of the top card of the Stock followed by a space and the number of other cards in parentheses with a '+' character in front of the number. For example DK (+17) is a Stock with the King of Diamonds at the top and 17 other cards (face down). If the Stock contains just one card - the top card - the same format is used, e.g., DK (+0). However, if the stock is empty, the string "empty" is returned instead.




That is the javadoc for the methods I need to implement in the Stock class. What I need is a nudge to get me started in the right direction. At first I thought I would need to create an array but since Im calling upon the Deck class I don't think I should need to create an array, right?
I do want to learn to code myself, but at the moment I cant even get my head around the simple methods outlined above.

Thanks for all the help so far

[Henry Wong]

At first I thought I would need to create an array but since Im calling upon the Deck class I don't think I should need to create an array, right?

Correct.

It is actually pretty straightforward. There is a one to one mapping between the methods that you need to write, and the methods of the Deck class. The only exception is the top() method, which probably need two calls to the Deck class.

Henry
[ May 07, 2006: Message edited by: Henry Wong ]

[Peter Brockway]

There is a one to one mapping between the methods that you need to write

To give you a "for instance":

public int numCardsRemaining() 
{
    return deck.numCardsRemaining();
}

[ May 07, 2006: Message edited by: Peter Brockway ]

[Richard Goodwinn]

Thanks

I thought I had it for a minute there. As I could of added these methods to class Deck.....

public void add(int i,Card c)
{
cards.add(i,c);
}

public void remove(int i)
{
cards.remove(i);
}

public Card getCard(int i)
{
return cards.get(i);
}


....and then called them in the Stock class like this...


public void addAtEnd(Card card)
{
deck.add(0,card);
}

public Card top() {
if(deck.numCardsRemaining() == 0)
{
return null;
}
else {
return deck.getCard(numCardsRemaining()-1);
}
}

public Card takeTop()
{
Card c = top();
deck.remove(numCardsRemaining()-1);
return c;
}


But then I realised that the assignement instructions say that we are not allowed to modify the Deck class.

Hmm looks like I need to think down a different path.

[ May 07, 2006: Message edited by: Richard Goodwinn ]
[ May 07, 2006: Message edited by: Richard Goodwinn ]

[Peter Brockway]

But then I realised that the assignement instructions say that we are not allowed to modify the Deck class.

I haven't looked at your code in detail (to see if it does what you want it
to do - I guess you can do that) but you should note that you haven't modified the Deck class. What you have done is use the Deck class, which seems to be the whole point of the exercise.

I've just had a look in more detail and you seem to regard the top of the Stock as the bottom of the Deck (and vice versa). This is fine if you are
consistent about it, and it is what you mean to do. (But, in the spirit of this forum, a method like takeTop() would get you shot in some saloons...)
[ May 07, 2006: Message edited by: Peter Brockway ]

[Peter Brockway]

I've just had a closer look at what you posted: and yes you do alter the Deck class, but you don't have to.

Unless there is some pressing reason not to, imagine the Stock's cards are in exactly the same order as the deck that it contains. The Stock methods you want can mostly just call the similar methods in Deck (like the example I posted before.)

The only tricky one (as Henry pointed out) is top(), where you have to get the card from the Deck, put it back, and then return it to the caller.

[Richard Goodwinn]

Oh ok thanks for that

I managed to get the addAtEnd method working fine, but am having a bit of trouble with the top and takeTop methods.

The takeTop method needs to return the card that was on top of the stock or null if the stock was empty. A call to the method also needs to reduce the number of cards remaining in the stock by one.

My attempts to make it work have been using an if statement. Is that the right way to be doing it? Because all my attempts have so far have either not compiled or just plain dont work.

Thanks

[Richard Goodwinn]

edited: never mind, I figure out what was wrong with my takeTop code.


[ May 09, 2006: Message edited by: Richard Goodwinn ]

[Richard Goodwinn]

From the javadoc...
public Card top()
the top card of the stock
returns: the top card of the stock, or null if the stock is empty. A call to this method does not remove the card from the top but just returns a reference to it.

How do I implement the top method so that it does not remove the top card but instead just return a reference to it?

[Garrett Rowe]

the get(int) method of java.util.List allows access to an element wothout removing it.

[Richard Goodwinn]

Also I am having a bit of trouble with the toString() method. It compiles but isnt passing the unit test.

The code I have for it is

public String toString() 
    {
        Card c = this.top();
        String s = c.suitToString() + c.pipToString() + " " + "(+" + (this.numCardsRemaining()-1) + ")";
        if (c == null)
        return "Empty";
        else return s;
    }

The suitToString() and pipToString() methods in there are from the Card class.

Any suggestions as to why that code isnt passing the unit test?
THanks

[Richard Goodwinn]

Any suggestions as to why my top() and toString() methods don't pass the unit test?

Thanks

[Peter Brockway]

How do I implement the top method so that it does not remove the top card but instead just return a reference to it?

Unfortunately the cards List of Deck is not accessible and you can't change the Deck class, so using the get(int) method seems to be ruled out. What I suggested before was:
(1) card from the Deck - use nextCard()
(2) put it back - use addAtStart()
(3) return the card to the caller - use return

It might seem strange that you can both put the card back at the top of the Deck and return it to the caller of top(). But remember a variable declared as a Card (and commonly called a Card) has as its value a reference to a Card object. Real cards can only be in one place at a time, but there can be lots of references to the same Card all over the place.

I am having a bit of trouble with the toString() method. It compiles but isnt passing the unit test.

How does it fail?

One problem I can see with your toString() method is that you call suitToString() etc even if c is null. This is not good. You should test if(c==null) straight after you call top(), and, if it is null, return "Empty" straight away.

[Richard Goodwinn]

Unfortunately the cards List of Deck is not accessible and you can't change the Deck class, so using the get(int) method seems to be ruled out. What I suggested before was:
(1) card from the Deck - use nextCard()
(2) put it back - use addAtStart()
(3) return the card to the caller - use return

Thanks for that. I've been busy for the past few days so havent had time to work on my project.
Ive been trying to add the addAtStart() method to my code but havent been successful. This is the approach I am using...

public Card top()
    { 
        if(deck.numCardsRemaining() == 0) 
        {
            return null;
        }
            else 
            {   
                return deck.nextCard(); 
                
            }      
            deck.addAtStart(Card);          
    }

That code doesnt actually compile, but Ive tried alot of different variations of that theme. Am I actually correct in using an if statement then adding the deck.addAtStart() method after the if statement?
I was trying to think of another approach I could use which uses both the nextCard() and addAtStart() methods but so far that is all I can come up with.

Maybe its just too early in the morning for my brain to be functioning

[Peter Brockway]

In your code:

public Card top()
{
if(deck.numCardsRemaining() == 0)
{
return null;
}
else
{
return deck.nextCard();

}
deck.addAtStart(Card);
}

you are returning too soon. (The compiler would have told you this). Think about introducing a new variable:

else {
    Card topCard;
    // use nextCard()
    // use addAtStart()
    // return
}

[Richard Goodwinn]

Thanks! I figured it out now.