Java array, NullPointerException?

问题

I declared two cards:

Card card1 = new Card('3', Card.Suit.clubs);
Card card2 = new Card('T', Card.Suit.diamonds);

This works:

Hand hand1 = new Hand();

hand1.takeCard(card1);

But why does this not work? It gives me a NullPointerException on second line:

Hand[] hand = new Hand[2];

hand[0].takeCard(card2);

回答1:

You are declaring an array of 2 hands. This is just setting up the array. You then need to instantiate the hand objects inside the array.

Say

hand[0] = new Hand(); 
hand[1] = new Hand();

回答2:

I think you need to go though this... I will clear your concepts... Please refer Java tutorials as and when possible.. its helpful

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/arrays.html

来源：https://stackoverflow.com/questions/15170192/java-array-nullpointerexception