linked list in java insert at end - nullpointerexception

Question

Guys I do have problem while inserting a new node at the end of a list. insert at begening works fine but in insert at end it shows null pointer exception.
Please look in method inserAtEnd and suggest me how to deal with it:
package linkedlist;
class Node{
Node next;
Object data;
Node(Object x)
{
data=x;
}
}
class LL
{
Node first;
LL(Node f)
{
first =f;
}
void insertAtBeg(Object x)
{
Node n= new Node(x);
n.next=first;
first=n;
}
void insertAtEnd(Object x)
{
Node n= new Node(x);
Node k;
k=first;
while(k!=null)
{
k=k.next;
}
k.next=n;
}
void print()
{
Node p=first;
while(p!=null)
{
System.out.print(p.data+"-->");
p=p.next;
}
}
}
public class LinkedList {
public static void main(String[] args) {
LL l = new LL(null);
l.insertAtBeg("Raj");
l.insertAtBeg("Am ");
l.insertAtBeg("I ");
l.insertAtBeg("100 ");
l.insertAtEnd("Hello");
l.print();
System.out.println("returned in main");
}
}

Answer 1

The problem is your loop is going till k is null, you want to go till k.next is equal to null. You could also solve it by having a variable for the last node(This is what is almost always done). The code I've provided fixes the problem without adding any new variables however:
void insertAtEnd(Object x) {
Node n= new Node(x);
Node k;
k=first;
while(k.next != null) {
k=k.next;
}
k.next=n;
}