WHY is it not def? PLZ HELP IT IS VERY SIMPLE!!

ok I have an obj called Cell, and i made a 2D array, and I try to rest eveycell,
What is wrong ???

Code:

---

package thegame;
class Cell {
    boolean occupied = false;
    char own = ' ';
}

/**
 *
 * @author joseph
 */
class Queendom {
    public static final int MAX_LENGHT = 400;
    Cell [][]Board = new Cell[400][400];
    private int lenght = 0;

public void reset(){
      for(int i=0;i<lenght;i++){
        for(int j=0;j<lenght;j++){
          Board[i][j].occupied = false;
          Board[i][j].own = ' ';
        }
      }
    }

---

now, I have in my main :

Code:

---

public class The_Game {
    public static void main(String[] args) {
        // TODO code application logic here
        Queendom Q = new Queendom();
        Q.reset();
    }
}

---

But the when I cal the Q.reset(), and it look at the Board[i][j].occupied = false; it fail, and says:

Exception in thread "main" java.lang.NullPointerException
at thegame.Queendom.reset(Queendom.java:33)
at thegame.The_Game.main(The_Game.java:17)


PLZ help me on this !!!!
Thanks a lot

I tried to compile your codes, but the compiler didnt throw me any NullPointerException... are you sure that it is your problem?

You don't actually say what line 33 of Queendom.java is!

I'll assume that it is "Board[i][j].occupied = false;" You will get a NullPointerException if Board[i][j] is null. Where did you think Board[i][j] was assigned a nonnull value? (for any i/j).

ya did you try to run it?
b/c it does compile, but could you run it too?
@pbrockway2:
That is it; I didnt access/ use any elements in Board yet, I just want to reset all the occupied values to false.

could any of you guys run this simple program?:rolleyes:

There's really no reason to run the program (and to do that we would have to add the bits you have left out). There's no reason because you have already told us what happens: you get a NullPointerException when you try and access the array elements.

By the way, you are accessing the array elements when you set occupied to false. This isn't a nit-pick, it's a very important point. The line:

Quote:

---

Board[i][j].occupied = false;

---

means "I want to access the Board array at element i/j, take the Cell which is there and set its occupied field to false". Now the runtime complains because Board[i][j] is null and you can't set the occupied field of something that doesn't exist.

The answer to the question I asked before is that - at the moment - you are not assigning the elements of the Board array nonnull values. And you have to do that to avoid the NPE. Probably in the Queendom constructor, or in the code that alters lenght.

-----

It really doesn't help to post code that doesn't correspond with the runtime stack trace. No way is the NPE occurring on line 33. And the reset() method itself doesn't do anything unless something is happening to lenght in code that you haven't posted.

Quote:

---

Originally Posted by just_java

Code:

---

class Queendom {
    public static final int MAX_LENGHT = 400;
    Cell [][]Board = new Cell[400][400];
    private int lenght = 0;

public void reset(){
      for(int i=0;i<lenght;i++){
        for(int j=0;j<lenght;j++){
          Board[i][j].occupied = false;
          Board[i][j].own = ' ';
        }
      }
    }

---

---

You variable 'lenght' is zero so your other faults won't even get executed. Keep them for another thread.

kind regards,

Jos

THANKS EVERYONE;
I reset length outside:
So indeed, length is 400;

So How should I fix it?
Thanks again

By assigning some nonnull values to the array elements.

Quote:

---

Originally Posted by just_java

THANKS EVERYONE;
I reset length outside:
So indeed, length is 400;

So How should I fix it?
Thanks again

---

You have an array of references to Cells but those references don't refer to cells yet; you have to do that yourself, as in Board[i][j]= new Cell(), for every element in that array.

kind regards,

Jos