Please help! Exception in thread "main" java.lang.NullPointerException

[Arutha2321]

Please could someone check my code and tell me where the problem is? Thanks.

/** DECK OF CARDS
  * created by Arutha2321
  */
 
  class Card {                				  // A playing card, with variables i - number of card, color - color of card, value - value of card.
    int i;
    String color;
    String value;
 
    public Card (int j, StringBuffer f, StringBuffer h) { // A constructor of a card.
	this.i = j;
	this.color = f.toString();
	this.value = h.toString(); 
    }
 
    public String showCard() {                       	  // A method that returns the color and value of a card in a string.
	return (this.color + this.value + "\n");
    }
  }
 
  class Deck {						  // A deck of card, with one variable cards, which is an array of instances of class Card.
    Card[] cards;
 
    public Deck() {
      String[] colors = {"heart", "spade", "diamond", "club"};
      String[] values = {"7", "8", "9", "10", "J", "Q", "K", "A"};
 
      StringBuffer co = new StringBuffer();               
      StringBuffer va = new StringBuffer();
 
      for (int i = 0; i < colors.length*values.length; i++) {    // This creates one Card for every combination of color and value.
	co.append(colors[i%colors.length]);
	va.append(values[i%values.length]);
	this.cards[i] = new Card(i,co,va);
      }
    }
 
    public void showDeck() {				 	 //A method that prints out all of the cards in the deck.
      for (int i = 0; i < colors.length*values.length; i++) {
	System.out.println(this.cards[i].showCard());
      }
    }
  }
 
  public class DeckOfCards {					// A class with the main function, that creates a deck and shows its content.
    public static void main(String[] args) {
      Deck deck1 = new Deck();
      deck1.showDeck();
    }
  }

Compilation goes all right, but when I want to run the program, I get this error message:

Exception in thread "main" java.lang.NullPointerException
               at Deck.<init>(DeckOfCards.java:34)
               at DeckOfCard.main(DeckOfCards.java:47)

[helloworld922]

You forgot to initialize the array of cards:

public Deck()
{
     Card[] cards = new Card[52];
     // rest of code
}

[Arutha2321]

Thank you very much.