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Thread: assigning problem

  1. #1
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    Default assigning problem

    I have created an array type pkt object of packet class to store a packet object pobj,and once passed to add method it is changed to dataInterest type and stored in the dlist[].....

    In my code when i assign an object reference nodeobj[0].pkt[0]=pobj the error comes Exception in thread "main" java.lang.NullPointerException
    at mhand.add(mhand.java:27)
    at mhand.main(mhand.java:18)

    public class mHand {
    	public node[] nodeobj;
    	public static void main(String[] args) {
    		node[] nodeobj=new node[2];
    		nodeobj[0]=new node(1,2);
    		nodeobj[1]=new node(6,6);
    		packet pobj=new packet(3,0);
    		mHand m=new mHand();
    		m.add(pobj);	 // ............................>line 18
    	public void add(packet pobj)
    		nodeobj[0].pkt[0]=pobj;   //......................................line 27
    		dataInterest dobj=new dataInterest(nodeobj[0].pkt[0].type,nodeobj[0].pkt[0].senderid);
    		System.out.println(dobj.type+"  "+dobj.id);
    		System.out.println("datalist has first object with type"+nodeobj[0].dlist[0].type);
    public class node {
    	int x;
    	int y;
    	node nlist[]=new node[5];
    	dataInterest[] dlist=new dataInterest[5];
    	packet[] pkt=new packet[1];
    	public node(){}
    	public node(int a,int b)
    public class Gradient {
    	int id;
    	public Gradient(int a)
    	public Gradient()
    public class packet {
    	int senderid;
    	int type;
    	public packet(int a,int b)
    i want to assign pkt[] for each nodeobj[0] and nodeobj[1].. so that each nodeobj has a unique pkt[] to store packet.
    Last edited by jack_nutt; July 4th, 2011 at 01:55 PM.

  2. #2
    Junior Member Mrc0d3r's Avatar
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    Default Re: assigning problem

    You get a java.lang.NullPointerException because you are trying to use public nodeobj array without creating their respective objects.
    //change the node[] to static so as to use it in main() method
    public static node[] nodeobj;
    //in the main() method change this line
    nodeobj=new node[2];

  3. The Following User Says Thank You to Mrc0d3r For This Useful Post:

    jack_nutt (July 4th, 2011)

  4. #3
    Super Moderator Norm's Avatar
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    Default Re: assigning problem

    If you make the variable static, make sure you don't want to have more than one instance of the mHand class, each with their own versions of nodeobj. When a variable is static, there will only be one version shared between all instances of mHand objects.

  5. The Following User Says Thank You to Norm For This Useful Post:

    jack_nutt (July 4th, 2011)

  6. #4
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    Default Re: assigning problem

    I'm getting a sense of deja-vue...

    In the code you posted, you have a class member node array called 'nodeobj' which never gets initialized and is hidden in the main(..) method by a local node array also called 'nodeobj' which does get initialized and has 2 nodes added to it, but which is not accessible by other class methods because it is local in scope.

    I'm pretty sure I went though all this in a previous thread, so I'm not inclined to spend any more time repeating myself.

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