Java简单BlackJack游戏，java.lang.NullPointerException

Question

I am writing a java program to make a simple blackjack game.

I am using an array of card objects as the users hand.

the user will be dealt two cards in their hand, however they can ask for another card until they reach a limit of 5 cards.

For this reason I have made the array of card objects with 5 slots to allow for the possibility of further cards being added to the hand.

However now I can't print the original hand when dealt or if the user does not ask for the full 5 cards because my array will have null objects.

What is the quickest, simplest and easiest way to fix this issue?

Answer 1

Place the line to print the value of the card inside an if statement that checks to see whether the array value is null. Something like:

for(int i = 0; i < cardArray.length ; i++)
{
  if(cardArray[i] != null)
      System.out.print(cardArray.value);
}

Answer 2

Don't use an array - use a List, perhaps an ArrayList.

Then, you can simply say:

for (Card card : hand) {
  System.out.println(card);
}

Where I'm assuming your Card class has a toString() method, and 'hand' is a List<Card>

Answer 3

You cannot, as you know, access anything inside of a null object. In this case, you should check each of the 5 cards if it is null when printing.

Answer 4

Check for null before you do anything:

if(x[i] == null){
    don't.do.anything();
}else {
    print.something();
}

The methods are fake obviously but try something like that.

But as the comment above says, you would be better off with a list.