I am confused

[prof.deedee]

Hi
When I wrote this code:
public class Main {

public class node {

int[] nod = {0, 0, 0};
}

public static node[] state = new node[4];
public static void divide(int[] M )
{
state[0].nod[0] = M[0];
state[0].nod[1] = M[1];
state[0].nod[2] = M[2];
state[1].nod[0] = M[3];
state[1].nod[1] = M[4];
state[1].nod[2] = M[5];
state[2].nod[0] = M[6];
state[2].nod[1] = M[7];
state[2].nod[2] = M[8];
state[3].nod[0] = M[9];
state[3].nod[1] = M[10];
state[3].nod[2] = M[11];
}

public static void main(String[] args) {
int[] M = {0, 1, 1, 1, 1, 1, 0, 1, 0, 0, 1, 0};
divide(M);


}
}


there is no error but when I try run it this message appear::eek::eek:

Exception in thread "main" java.lang.NullPointerException
at cry.Main.divide(Main.java:21)
at cry.Main.main(Main.java:37)
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)

what it means ???:confused::confused:

[mrmatt1111]

public static node[] state = new node[4];

creates an array of size 4, but you still need to call the constructor and create the actual object for each of those four.

node[0] = new Node();
node[1] = new Node();
node[2] = new Node();
node[3] = new Node();

[prof.deedee]

I can't understand u..could you please explain more..
first I create object node which contain array of integer nod this array length is 3

then I create array from that object node its name state and this array length is 4

so where should I put the constructor ..
thanks

[Fubarable]

.... um, he showed you where to put the calls to the Node constructor.

[prof.deedee]

sorry sir but I am new in Java so can you tell me exactly where I should but that call

and I don't have Node type it's node
did you mean
state[0]=new node();

[Fubarable]

It should be Node as class names should begin with a capital letter. I recommend you change it.

After you declare your array of four Nodes, but before you use them, use a for loop to loop through the array and initialize each Node in the array by calling the Node constructor.

for (int i = 0; i < state.length; i++) {
  state[i] = new Node();  // again, the Node class should be capitalized.  
}

This could be done in the main method, at the top.

Much luck.

[prof.deedee]

Thank u so much