Linked List Java

Question

this is a homework problem, but not really to be graded, just something to be used in future projects. I'm having problems with getting to display what I have in my list/nodes. Mainly I get an error when calling displayList.

Merge combines lists into new one which includes all list 1 and 2 items.

Union includes only one of each duplicate from list 1 and 2.

Intersection only includes duplicates from list 1 and 2, not from same list.

Note in merge method the code in note form is just an alternative form of current one I believe.

//Kevin Clement
//Homework 2

   class LinkedListHomework
   {
      public static ListNode Merge(ListNode List1, ListNode List2)
      {
         ListNode head, tail;
         head = tail = new ListNode( "Hi1");

         while(List1 != null && List2 != null)
         {
            if(List1.getItem().toString().compareTo(List2.getItem().toString()) < 0)
            {
               tail.setNext(new ListNode(List1.getItem()));
               List1 = List1.getNext();
            }
            else
            {
               tail.setNext(new ListNode(List2.getItem()));
               List2 = List2.getNext();
            }
            tail = tail.getNext();
         }

      // while(List1 != null)
      // {
      // tail.setNext(new ListNode(List1.getItem()));
      // tail = tail.getNext();
      // List1 = List1.getNext();
      // }
      // 
      // while(List2 != null)
      // {
      // tail.setNext(new ListNode(List2.getItem()));
      // tail = tail.getNext();
      // List2 = List2.getNext();
      // }
         return head.getNext();


      }




   // public static ListNode Union(ListNode List1, ListNode List2)
   // {
   // 
   // 
   // 
   // }

   // // public static ListNode Intersection(ListNode List1, ListNode YList2)
   // {
   // 
   // }

      public void displayList()
      {
         ListNode temp = head;
         System.out.print("head");
         while(temp != null)
         {
            System.out.print("--> " + temp.getItem());
            temp = temp.getNext();
         }
         System.out.print("\n\n");
      }


      public static void main(String args[])
      {

         ListNode A = new ListNode("Adam", new ListNode("Andrew", new ListNode("Kyle", new ListNode("Luc", new ListNode("Michael", new ListNode("Tony"))))));
         ListNode B = new ListNode("Adam", new ListNode("Fallon", new ListNode("Jim", new ListNode("Kyle", new ListNode("Nina", new ListNode("Shea", new ListNode("Tony")))))));

         displayList(A);
         A.displayList();




      }

   }

Okay here are my errors, I feel that copying them down will be more helpful to you guys than me trying to explain what's wrong.

LinkedListHomework.java:61: cannot find symbol  
symbol  : variable head 
location: class LinkedListHomework  
         ListNode temp = head;  
                         ^  
LinkedListHomework.java:78: displayList() in LinkedListHomework cannot be applied to (ListNode)
         displayList(A);  
         ^  
LinkedListHomework.java:79: cannot find symbol  
symbol  : method displayList()  
location: class ListNode  
            A.displayList();  
             ^  
3 errors

Formatting, formatting, formatting. It really does pay out (for instance, after this comment, I shall leave this question because, if you don't show hubris... not worth it for me ;-) — user166390
– user166390, Commented Oct 28, 2011 at 3:09
What @pst said. If you want to ignore formatting guidelines, you'd better be enough of a badass to not need to ask for help. — ObscureRobot
– ObscureRobot, Commented Oct 28, 2011 at 3:12
Please explain formatting, what is wrong with my formatting? I'll happily change it if I knew. Also will edit my question because i left out parts. sorry. — Kevin Clement
– Kevin Clement, Commented Oct 28, 2011 at 3:15
@KevinClement Indentation shows structure and aids in communicating intent. — Dave Newton
– Dave Newton, Commented Oct 28, 2011 at 3:19

Matt Fenwick · Accepted Answer · 2011-10-28 03:47:46Z

1

The first error is with the line ListNode temp = head; : head has not been declared.

The second error is because you're trying to call displayList with an argument: it takes no arguments. Also, it's not a static method -- it must be called on an object.

The third error is because you're trying to call displayList on an object of class ListNode, while displayList actually belongs to class LinkedListHomework.

edited Oct 28, 2011 at 3:47

answered Oct 28, 2011 at 3:40

Matt Fenwick

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1 Comment

Dave Newton Over a year ago

And trying to call an instance method from a static method.

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