Skipping one value when storing into an array

Question

Can someone help me check ?

error:

java.lang.NullPointerException

How do I remove this error ?

my main Class:

public class deck {

    public static void main(String[] args) {
        Deck app = new Deck();
        app.Deck();
    }

}

my Deck class:

    public class Deck {
    public int TOTALCARDS;
    Card[] d;
    public int nH;


    public void createDeck() {
            String[] suitsArray = new String[4];

            for(int i=0; i<numArray.length; i++) {
                numArray[i] = i+1;
            }

            for (int i=0; i<13; i++) { 
                if (i!=11){
                deck[i+25] = new Card(suitsArray[2], i+1);
                }
                else if(i > 10){
                    deck[i+25] = new Card(suitsArray[2], i+1);
                }
                }
    for (int i=0; i<13; i++) {
        deck[i+25].display();
    }
}

This is the Card Class.

public class Card {

        public String suit;
        public int number;


        public Card(String s, int n){
            this.suit = s;
            this.number = n;
        }


        public String words;
        public String getTitle(){
            String 
            if (number == 1){
                words = " Ace";

            }
            else if (number ==3){
                words = " Three";
            }
            else if (number ==4){
                words = " Four";
            }
            else if (number ==5){
                words = " Five";
            }
            else if (number ==6){
                words = " Six";
            }
            else if (number ==7){
                words = " Seven";
            }
            else if (number ==8){
                words = " Eight";
            }
            else if (number ==9){
                words = " Nine";
            }
            else if (number ==10){
                words = " Ten";
            }
            else if (number ==11){
                words = " Jack";
            }
            else if (number ==12){
                words = " Queen";
            }
            else if (number ==13){
                words = " King";
            }
            displayTitle = suit + words;
                    if (displayTitle.equalsIgnoreCase("Diamond Queen")){
                        displayTitle= "DIAMOND QUEEN";
                    }


        return (displayTitle);

    }

        public void display(){
            System.out.println("< " + get() + " >");
        }
    }

When I run the code I got

Hearts Ace
Hearts Two
Hearts Three
Hearts Four
Hearts Five
Hearts Six
Hearts Seven
Hearts Eight
Hearts Nine
Hearts Ten
Hearts Jack
Exception in thread "main" java.lang.NullPointerException
    at Deck.createDeck(Deck.java:57)
    at Deck.<init>(Deck.java:9)
    at deckMain.main(deckMain.java:5)

Answer 1

EDIT: See the comment by Kick Buttowski below, this is at best a partial answer.

---

You're calling Card.display()

for (int i=0; i<13; i++) {
    deck[i+25].display();
}

Which in turn calls Card.getTitle()

public void display(){
    System.out.println("< " + getTitle() + " >");
}

The problem lies there:

public String getTitle(){
    String displayTitle = suit + words; // <-- Problem
    if (number == 1){
        words = " Ace";
    }
    // ...

At the marked line, words is not set yet, so it's null. Accessing its value will raise a NullPointerException.

As Takendarkk pointed out, you can overcome this with minimal changes to your code by initialising it either in your constructor or in the declaration:

public class Card {
    // ...
    String words = "";

Or, since (as far as we know) words is only used within display(), move it there:

public void display() {
    String words = ""; // Still need to be initialised
    // ...

Answer 2

EDIT: Your card size is 51 ... it should be 52

if (i!=11){
    deck[i+25] = new Card(suitsArray[2], i+1);
}
else if(i > 11){
    deck[i+25] = new Card(suitsArray[2], i+1);
}

This doesn't add up, what if i = 11?? You do nothing as

i!=11 =  false and i > 11 == false;

this means the else if (i > 11) will never execute. also your code does the exact same thing??

if you are trying to initalise all 52 cards you can do something like:

for (int i=0;i<deck.size;i++) {
   deck[i] = new Card(suitsArray[i/13], numArray[i % 13]);

EDIT: after more of an explanation of what you are doing .....

for (int i=0, j=0;j<deck.length;i++) {
    if ((i/13) == 2 && (i%13) == 11)
        continue;
    deck[j++] = new Card( suitsArray[i/13], (i % 13));
}

also in card have (much clearer) static String[] titles = {"Ace", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King"}; and

public String getTitle() {

        return suit + " " + titles[number];

}

Answer 3

It is because your value at deck[11] is null because you skipped putting an instance of Card at that index.

edit: [should be deck[i + 25]], where i = 11;

Regarding the answers pointing to the variable word being null as reason of NPE. I doubt this. I have tried the code in my machine and it is not giving me NPE. (see also Concatenating null strings in Java)