CODEWITHSUNDEEP
javaexceptionarraylistnullnullpointerexception
Samuel Nguyen
Samuel Nguyen

Reputation: 29

NullPointerExceptions on arraylist

I am trying to make a snake-type game in Java.

To do so, I am using lists to keep hold every of the snake's body parts with

ArrayList<SnakeBodyPart> snakeBodyParts = new ArrayList<SnakeBodyPart>();.

I declare and initiate a variable, SnakeBodyPart SnakeBodyPart = null;.

I then add a body part to the snake with snakeBodyParts.add(SnakeBodyPart);.

(Not the most efficient way, I guess, but it'll have to do.)

But for some reason, whenever I run the script, I get

Exception in thread "main" java.lang.NullPointerException,

and that the error is

at game.Snake.<init>(Snake.java:60)

in the Java console.

I want to know what the problem is. Here is the code for the SnakeBodyPart.

class SnakeBodyPart{
    int x,y,direction;
    void move(){
        if(direction == 0){
            y -= 50;
        }
        if(direction == 1){
            x += 50;
        }
        if(direction == 2){
            y += 50;
        }
        if(direction == 3){
            x -= 50;
        }
    }
}

Thanks in advance!

EDIT:

Line 60 is snakeBodyParts.get(0).direction = 0;.

Upvotes: 0

Views: 89

Answers (1)

Rahul
Rahul

Reputation: 3519

You have done this:

  SnakeBodyPart snakeBodyPart = null;

Create the object

  SnakeBodyPart snakeBodyPart = new SnakeBodyPart();

Since snakeBodyPart is null, you are getting NullPointerException in Line 60. You are calling get() method on null as snakeBodyParts.get(0).direction = 0;

Upvotes: 1

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