Help with NullPointerException

[chrisxon]

I am having a difficulty with a piece of code, it is causing a nullpointerexception and its because my variable is being returned as null, help anyone?

public void newGame()
{
this.theDeck = new Deck();
this.piles = new Pile[Constants.NUM_PILES];
Card tempCard2;

for (int i=Constants.FIRST_LAYOUT_PILE; i <
Constants.NUM_LAYOUT_PILES ; i++)
{
for (int x = 0; x < Constants.initalCardsOnPile(i); x++)
{
tempCard2 = theDeck.dealACard();
this.piles.addACard( tempCard2 );
}
}
}


public void addACard(Card c)
{
cards.addElement(c);
}


public Card dealACard()
{
return cards[curCardIndex++];
}

 

[Diancecht]

No way to know without the stacktrace or any hint of where it's happening.

Cheers,
Dian

 

[timw]

I can't see where the 'cards' reference is declared / initialised. What is it? You seem to be using it both like an array and like a List instance. It can't be both.

Tim

 

[chrisxon]

public class Deck
{
Card[] cards;
int curCardIndex;
public Deck()
{

int i = 0;
cards = new Card[ Constants.NUM_CARDS_IN_DECK ];
curCardIndex = 0;

//Loops to the amount of cards in a deck
for(int iSuit = 0; iSuit < Constants.LAST_SUIT; ++iSuit)
for(int iRank = 0; iRank < Constants.NUM_CARDS_PER_SUIT ; ++iRank)
{
//Places a random card from the ordered deck into the mixed deck
this.cards[i++] = new Card(iRank,iSuit);
}

//Calls the shuffel function to mix up the ordered deck
shuffle();

}

/*Takes the ordered deck created in the deck() method and
mixes it into a new deck, named mixedDeck, and pus them into a
random order.*/
public void shuffle()
{
int randomNumA = 1;
int randomNumB = 1;
Card tempCard;


//Loops to the amount of cards in a deck
for(int x = 0; x < Constants.NUM_CARDS_IN_DECK; ++x)
{
//Creates a random number between 0 and 51
randomNumA = (int) (Math.random()*(Constants.NUM_CARDS_IN_DECK));
randomNumB = (int) (Math.random()*(Constants.NUM_CARDS_IN_DECK));
//Places a random card from the ordered deck into the mixed deck
tempCard = cards[randomNumA];
cards[randomNumA] = cards[randomNumB];
cards[randomNumB] = tempCard;

}
}

/*Deals a card into the play field*/
public Card dealACard()
{
return cards[curCardIndex++];
}

}


When the line "cards[curCardIndex++} executes it is being returned as null. I am not sure why it is doing that

 

[stefanwagner]

your curCardIndex isn't private, so it might be modified outside your class, or you call dealACard() more often, than cards are in your stack.

By the way: Stack.
Why don't you use a stack?

seeking a job as java-programmer in Berlin:

http://home.arcor.de/hirnstrom/bewerbung

 

[tdelamater]

change your incriment operators from prefix to postfix.

//Loops to the amount of cards in a deck
for(int iSuit = 0; iSuit < Constants.LAST_SUIT; iSuit++)
   for(int iRank = 0; iRank < 
      Constants.NUM_CARDS_PER_SUIT;iRank++){
      //Places a random card from the ordered deck 
      //into the mixed deck
      this.cards[i++] = new Card(iRank,iSuit);
   }

 

[tdelamater]

By the way: Stack.
Why don't you use a stack?

I'd imagine you wouldn't use a stack because when you think of a deck of cards as an object you might want to pick up the stack, split the stack in two, and shuffle from the bottom.

 

[stefanwagner]

change your incriment operators from prefix to postfix.

That's nonesense.
Since there is no assignement in the expression, this will have exactly zero effect.

seeking a job as java-programmer in Berlin:

http://home.arcor.de/hirnstrom/bewerbung

 

[timw]

Why don't you just hold all your Card instances in a List (eg. ArrayList) and use the java.util.Collections.shuffle(List) method to shuffle them? Much easier than an array.

Tim