Recieving an Exception Error

[Michael Coco]

First post here and am I am using Eclipse and am receiving the following error:

Exception in thread "main" java.lang.NullPointerException
at Hw1.createrandoms(Hw1.java:26)
at Hw1.main(Hw1.java:16)

By the way the errors at 8 and 18 below

I know java fairly well, but for whatever reason i cannot figure out what im doing wrong.

My code

    
public static void main(String[] args) 
	{
		// TODO Auto-generated method stub
		int N = 0;
		Random rand = new Random();
		N = rand.nextInt(901) + 100;
		createrandoms(N);
		for (int i = 0; N>i; i++)
			System.out.println(OriginalList[i]);
	}
	
	public static void createrandoms(int N)
	{
		int Location = 0, freeCount = 0, i, skip;
		for (i=0; N>i; i++)
		{
			OriginalList[i] = 0;
		}
		Location = 1;
		freeCount = N;
		for (i=0; N>i; i++)
		{
			skip = (int) (freeCount * Math.random() + 1);
			while (skip > 0)
			{
				Location = (Location % N) + 1;
				if (OriginalList[Location] == 0)
				{
					skip = skip - 1;
				}
			}
			OriginalList[Location] = i;
			freeCount = freeCount - 1;
		}
	}	

Thanks in advance

[Gamini Sirisena]

Have you initialized the OriginalList variable?

[Michael Coco]

sorry forgot this

public static int[] OriginalList;

have it inside my public class

[Gamini Sirisena]

Ok. You have declared the variable. Where are you initializing it?

[Michael Coco]

I guess i havent initialized OriginalList... can you give me some hints on how? I tried int[] OriginalList = new int[N];

im much better with vb and c#, sorry

[Michael Coco]

Sorry it seems as if i move

  		
		OriginalList = new int[N];
for (int i=0; N>i; i++)
		{
			OriginalList[i] = 0;
		}  

before i call createrandoms(N-1) it will work properly. Can someone tell me why? why cant i initialize after i call create randoms?

[Campbell Ritchie]

You will escape the NullPointerException wherever your initialisation is, provided it is before you try to use the reference. It is probably better design to initialise every instance field in your constructor.

[Campbell Ritchie]

And why have you got all your methods static? You have got too much inside your main method. You ought to be creating an object, then calling instance methods on it.

[Michael Coco]

Campbell Ritchie wrote:And why have you got all your methods static? You have got too much inside your main method. You ought to be creating an object, then calling instance methods on it.

No real reason, just how i set it up. When it tried calling createrandoms, i had to create it as static or i kept receiving an error