Question

Background: my assignment was to write a program that uses linked list to keep track of cards in a card game (war). So I wrote 4 programs: card.java, deckofcards.java, hand.java, war.java(driver). card holds basic info. When adding to a linked list of the cards I use a method called setLast:

nextCard=null;
public card(String a, String b)
{
    hand=a;
    suit=b;
}
public void setLast(card c)
{
    if(nextCard==null)
    {
         nextCard = c;
    }
    else
    {
         nextCard.setLast(c);
    }
}

then in deckofcards.java:

    card deck, dealt;
    public deckofcards()
{
    rand = new Random();
    dealt = new card("0","0"); //null card place holders
    first = new card("0","0");
    numcards = 52;
    shuffle();
}
    public card dealCard()
{
    card c=new card("0","0");
    if(first!= null)
    {
        c = first;
        first = first.nextCard;
        c.nextCard = null;
        if(dealt.toString().compareTo("00")==0)
        {
            dealt = c;
        }
        else
        {
            dealt.setLast(c);
        }
        numcards--;
    }
    else
    {
        System.out.println("Deck: ran out of cards");
    }
    return c;
}

so deckofcards generates 52 randomly(supposed to anyway, but thats a different question) ordered cards and hands deals them to instances of hand.java in war.java

hand.java:

    card cards;
    int numcards;
    public void getCard(card c)
{
    System.out.println("In hand.java,getCard");
    if (numcards==0)
    {
        cards = c;
        numcards++;
    }
    else
    {
        cards.setLast(c);
    }
}

and war.java:

    players = new hand[numplayers];
    for(int i=0;i<numplayers;i++)
{
    players[i] = new hand();
}
deck = new deckofcards();
int i=0;
while(i<52)
{
    int ii=0;
    if((ii<numplayers)&&(i<52))
    {
        players[ii].getCard(deck.dealCard());
        i++;
        ii++;
    }
    else
    {
        ii=0;
    }
}

output:
In hand.java,getCard
In hand.java,getCard
Exception in thread “main” java.lang.StackOverflowError
at card.setLast(card.java:125)
at card.setLast(card.java:125)
at card.setLast(card.java:125)
at card.setLast(card.java:125)
at card.setLast(card.java:125)
at card.setLast(card.java:125)
at card.setLast(card.java:125)
//repeated 1000s of times…

Of course I only provided the snippet of code I believe is causing the problem I can provide the whole code upon request.

Answer 1

Your list has a loop somewhere, i.e. “A->B->C->D->B”. Is there a reason you are using “null card placeholders” instead of the value null? I notice setLast is checking for the value ‘null’ instead of ’00’ for your null placeholder, but without seeing all the code it’s hard to tell where your list gets a loop at.