Java, non-static cannot be reference to static context

Question

Doing Java course, at UNI atm, and I'm having a bit of trouble with a dice-problem.

I have the following:

 public class Die {
   public int eyes;
   private java.util.Random r;
   private int n;

   public Die (int n) {
     r = new Random();
     this.n = n;
   }

   public void roll() {
     eyes = r.nextInt(Die.n);
   }

When compiling I get: non-static variable n cannot be referenced from a static context. How would I go about fixing this, whilst having it randomize from a user given value?

Take a look at this question's answers: http://stackoverflow.com/questions/2559527/non-static-variable-cannot-be-referenced-from-a-static-context .... Of course the question's code is a bit different and less concise, but the answers should still help you. — rodamn, Sep 15 '15 at 20:56

score 3 · Accepted Answer · answered Sep 15 '15 at 20:55

3

n is not a static variable, so you cannot refer to it in a static manner (Die.n).

Since it is an instance variable in the Die class, and you are referring to it in the Die class, you can just use n instead of Die.n.

answered Sep 15 '15 at 20:55

Evan LaHurd

977
2
14
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Thank you very much! This doesn't completely solve the problem though, seeing as I then get java.lang.NullpointerException: null, in the terminal. – Rasmus Hjorth Lüdeking Sep 15 '15 at 21:02
1

How are you calling `roll()`? You should be creating a new `Die` object by using `Die die = new Die(6);` (or whatever number you want), then you would call `die.roll();`. – Evan LaHurd Sep 15 '15 at 21:04
1

I'd probably also use `r.nextInt(n) + 1` otherwise you could get 0, which doesn't make sense for a die. – Evan LaHurd Sep 15 '15 at 21:10
Added `Die die = new Die();` to the contructor, still getting nullpointer – Rasmus Hjorth Lüdeking Sep 15 '15 at 21:11
1

The line `Die die = new Die();` won't compile since you do not have a no argument constructor for `Die` class. – Sandeep Chatterjee Sep 15 '15 at 21:13

score 1 · Answer 2 · answered Sep 15 '15 at 20:52

1

Remove

Die.n

and change it to simply

If n were declared static, you could use the both notations, even though the first one would be redundant (because you're from the inside of containing class)

answered Sep 15 '15 at 20:52

Luigi Cortese

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6
37
48

Java, non-static cannot be reference to static context

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