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)

Code :

---

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);
		nodeobj[0].dlist[0]=dobj;
		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)
	{
		x=a;
		y=b;
 
 
	} 		
 
}
 
 
public class Gradient {
	int id;
 
 
	public Gradient(int a)
	{
		id=a;
 
	}
	public Gradient()
	{
 
 
	}
}
 
 
 
public class packet {
 
	int senderid;
	int type;
	public packet(int a,int b)
	{
		type=a;
		senderid=b;
 
	}
 
 
 
}

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i want to assign pkt[] for each nodeobj[0] and nodeobj[1].. so that each nodeobj has a unique pkt[] to store packet.

You get a java.lang.NullPointerException because you are trying to use public nodeobj array without creating their respective objects.

Code Java:

---

//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];

---

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.

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.