Add to a "null" list in java

Question

I am trying to add an item to a list of card objects, and I get a nullpointer exception if I run this code. I believe I can't add to a 'null' list, but how do I fix this? (The error occurs at 'cards.add(...);')

public class Deck {

    private List<Card> cards;
    public Deck(String[] ranks, String[] suits, int[] values) {
        for (int i = 0; i < ranks.length; i++) {
            for (int j = 0; j < suits.length; j++){
                cards.add(new Card(ranks[i], suits[j], values[i]));
            }
        }
    }

You have declared `cards` as a reference to a `List`, but you have not assigned it to refer to any actual object. It looks like you want to create an appropriate object and assign a reference to it, maybe: `cards = new ArrayList<>();`. — John Bollinger, Dec 06 '17 at 19:50

score 4 · Accepted Answer · answered Dec 06 '17 at 19:50

4

You need to initialize your list...

private List<Card> cards = new ArrayList<>();

answered Dec 06 '17 at 19:50

Gaskoin

2,469
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Thank you, I tried doing that but must have used the wrong syntax. – Yuri Dec 06 '17 at 19:55

score 2 · Answer 2 · answered Dec 06 '17 at 19:51

2

Initialize the List cards as follows with the specified element type:

private List<Card> cards = new ArrayList<Card>();

answered Dec 06 '17 at 19:51

Funsaized

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from Java 7 diamond operator <> was introduced to add type inference and reduce verbosity: new ArrayList<>(); – Lakshya Srivastava Jul 27 '20 at 15:21

Add to a "null" list in java

2 Answers2