CODEWITHSUNDEEP
javacollectionslinked-list
Orphid
Orphid

Reputation: 2852

Java: Initializing a new LinkedList Collection

I am trying to build a simple card game as a personal exercise. I have a collection Cards that should contain my deck. To initialize it, I want to pass it a map of what the deck should look like - an integer array (1 to n, 1 to 2) with (n, 1) containing a card type which is resolved within the card class, and (n, 2) containing the number of cards that type I want in the deck. I'm having difficulties with a NullPointer exception, however. Here is my Cards class:

import java.util.LinkedList;

public class Cards{
    private LinkedList<Card> CardDeck;

  ...

    public boolean MakeDeck(int[][] DeckMap){
        /*feed the function a 2D int array (0 to n, 0 to 1)

        @Param - DeckMap[][] - [n][0] to contain card type
        [n][1] to contain DupeCount*/

        //search the array for duplicates
        for (int i = 0; i < DeckMap.length; i++){
            int hold = DeckMap[i][0];
            DeckMap[i][0] = -10;
            for (int j = 0; j< DeckMap.length; j++){        
                if (DeckMap[j][0] == hold){
                    DeckMap[i][0] = hold;
                    return false;
                }       
            }
            DeckMap[i][0] = hold;
        }

        //Add the cards
        // tried variations on this: CardDeck = new LinkedList<Card>;
        for (int i = 0; i< DeckMap.length; i++){
            Card cC = new Card();
            cC.initializeCard(DeckMap[i][0], DeckMap[i][1]);
            CardDeck.addLast(cC);
        }
        return true;


    }
}

The NullPointer error occurs at the cC.addLast line - since I have initialized the Card class, the Null Pointer should refer to the CardDeck LinkedList I want to add the Card to, I think. But I can't work out how to initialize the list. Or is the .initializeCard call the problem (code below)? Thanks in advance for your help and apologies if I've missed something obvious.

Error:

java.lang.NullPointerException at towergame.Cards.MakeDeck(Cards.java:75)

  public class Card {

        private static String cName;
        private static int cDuplicateCount;
        public static cEffect myEffects;

        public final void initializeCard(int inEffect, int DupeCount){
            myEffects = new cEffect();
            myEffects.setEffect(inEffect);
            cName = myEffects.getCardType();
            cDuplicateCount = DupeCount;
        }
     ...
   }

Upvotes: 0

Views: 4334

Answers (1)

Arjit
Arjit

Reputation: 3456

Instead of this private LinkedList<Card> CardDeck;

use this private LinkedList<Card> CardDeck = new LinkedList<Card>();

it is throwing NPE because cardDeckhas not been initialized.

Upvotes: 2

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