adding a node at the end of a Linked List (java)

Question

This is my code for the linked list (not the main). The method "addLast" gives me the following error and i'm not sure how to resolve it: "non-static variable cannot be referenced from a static context". It is talking about this line: return new Node(x,null); I'd appreciate any help as to how to resolve this issue. Thank you

public class LinkedList
{
 private class Node 
 { 
 int item;
 Node link;
 public Node ()
 {
 item = Integer.MIN_VALUE;
 link = null;
 }
 public Node (int x, Node p)
 { 
 item = x;
 link = p;
 }
 } //End of node class
 private Node head;
 public LinkedList()
 {
 head = null;
 }
 //adds a node to the start of the list with the specified data
 //added node will be the first node in the list
 public void addToStart(int x)
 {
 head = new Node(x, head);
 }
 //adds a number at end of list 
 public static Node addLast(Node header, int x)
 { 
 // save the reference to the header so we can return it. 
 Node ret = header; 
 // check base case, header is null. 
 if (header == null) { 
 return new Node(x, null); 
 } 
 // loop until we find the end of the list 
 while ((header.link != null)) { 
 header = header.link; 
 } 
 // set the new node to the Object x, next will be null. 
 header.link = new Node(x, null); 
 return ret; 
 }
 //displays the list
 public void printList()
 {
 Node position = head;
 while(position != null)
 {
 System.out.print(position.item + " ");
 position = position.link;
 }
 System.out.println();
 }
}

Answer 1

Here are two solutions:

Make Node a static nested class:

private static class Node { ... }

Or, make the addLast method an instance method:

public Node addLast(Node header, int x) { ... }

• Chris Dodd: It doesn't need to be a static nested class, though it may make sense for it to be so. Making it non-static is irrelevant to the OPs problem.
• August: @ChrisDodd True, it's not absolutely necessary, but it seems more logical for Node to be independent of LinkedList.
• Chris Dodd: Depends on what you want to do with the list. Making it non-static allows the Node to refer back to the head of the list it is contained in, which may be useful for some algortihms.

Answer 2

Remove the static qualifier from addLast -- it needs to be non-static to have a list to add to the end of. It also should not take (or return) a Node, as Node is a private nested class, so code outside this class doesn't know (or care) what a Node is, so can't have one to pass.

public void addLast(int x) {
 if (head == null) head = new Node(x, null);
 else {
 Node p = head;
 while (p.link != null) p = p.link;
 p.link = new Node(x, null); } }

• Eternal Punishment: I can't because addLast will have to be static in order for my main to access it.
• Chris Dodd: No, your main just needs a LinkedList to call addLast on -- list = new LinkedList(); list.addLast(5); list.addLast(6);...
• Eternal Punishment: can you please explain the for loop?
• Chris Dodd: It scans to the end of the list. Rewritten as a while to make it clearer
• Eternal Punishment: so when i type in your code, for the line head = new Node (x); it gives me the following error : no suitable constructor found for Node(int)

Answer 3

The answer is in the error line:

non-static variable cannot be referenced from a static context

Remove the static for the method addLast.

public Node addLast(Node header, int x) 
{
 ....
}