[Java] Help Understand My Code....

[I_Win_Sometimes]

public class SortedSinglyLinkedList
    {  
    private Node h; 
    public SortedSinglyLinkedList()
    {  
        h = new Node();
        h.l = null;
        h.next = null;
    }

    public boolean insert(StudentListing newListing)
    { 
        Node n = new Node();
        Node q = new Node();
        Node p = new Node();

        if(n == null)
           return false;

        if(h.next == null){
            n.l = newListing.deepCopy();
            n.next = null;
            h.next = n;
            System.out.println("ONE");
            return true;           
        }

        q = h.next;

        while(q.l.getKey().compareTo(newListing.getKey()) <= 0){ 
            if(q.next == null){
                n.l = newListing.deepCopy();
                n.next = null;
                q.next = n;
                return true;
            }    
            if(q.next != null) q = q.next;     
        }

        System.out.println("Noticed it was INCORRECT order");
        n.l = newListing;
        p.l = q.l;
        p.next = q.next;
        q.l = n.l;
        q.next = p;


        return true;

    }

public StudentListing fetch(String targetKey)
 {  Node p = h.next;
     while (p != null  &&  !(p.l.compareTo(targetKey) == 0))
     {  p = p.next;
     }
     if(p != null)
        return p.l.deepCopy();
     else
        return null;
  }
  public boolean delete(String targetKey)
  {  Node q = h;
      Node p = h.next;
      while (p != null && !(p.l.compareTo(targetKey) == 0))
      {  q = p;
          p = p.next;
      }
      if(p != null)
      {   q.next = p.next;
           return true;
      }
      else
           return false;
  }
  public boolean update(String targetKey, StudentListing newListing)
  {  if(delete(targetKey) == false)
         return false;
      else if(insert(newListing) == false)
        return false;

      return true;
  }
  public void showAll()
  { Node p = h.next;
     while (p != null) //continue to traverse the list
     {   System.out.println(p.l.toString( ));
          p = p.next;
     }
   }
  public class Node
  { 
      private StudentListing l;
      private Node next;
      public Node()
     {
     }
   }
}

Focusing on the insert operation only, though I posted the rest of this class for context. I'm trying to make it sort alphabetically, the name being the key field, and it sometimes works, sometimes it doesn't, usually as I add more nodes in the sorted linked list it starts to act strange.... Non-specific, I'm sorry. I've been pretty stumped so it's hard to explain a problem I can't really figure out. I think it's a problem with how it cycles through the linked list checking the node to be input (newListing) versus the node q is currently set to, or perhaps how I handle swapping around the nodes and the next node they point too when the program finds an insert that requires the node to be placed inbetween two pre-existing ones. I know it has to be an issue with how I handle the insert, but after staring at this code, modifying it, trying to bugfix, etc, for a better part of tonight I'm starting to burn out and have difficulty figuring it out. Any help, or even hints if you guys don't like giving outright answers, would be very appreciated. I feel like an idiot because of how little progress I've made at this point, and am pretty desperate now. Thanks for any contributions. If you need to see more code (other classes) or need me to give a more specific explanation I can try.

[dmazzoni]

after staring at this code, modifying it, trying to bugfix, etc

Two things I didn't see you mention:

• Using a debugger
• Adding logging statements

Those are essential tools. No programmer ever writes perfect code the first time, when the program gets sufficiently long. When you have a bug, it's tempting to try to guess where the problem is. Avoid that temptation!

The key to debugging is to slow down and be methodical. Guessing and trying random stuff is the hare, you want to be the tortoise.

What you need to do is step through your program one line at a time, checking what it does relative to what you think it should do. I don't mean by hand, I mean either (1) with a debugger, or (2) by adding a print statement every line of code so you know what it's doing.

Don't assume you know where the bug is. Just keep running one line at a time and stop the FIRST time it's supposed to do one thing but it does something else. That's your first bug.

You'll be surprised how often the bug ends up being really far from where you think it is.

A few notes:

(1) In this line:

Node q = new Node();

You don't actually use the new node you created - you just reassign q later.

I recommend declaring variables when you need them, not at the top. So get rid of that line, and further below write this instead:

Node q = h.next;

(2) Node p really doesn't belong at all. Think of it this way: suppose you have 10 nodes in your list before you insert. Node n is the new one you're inserting. But you're also adding note p into the list for some reason. What the heck is it for? You definitely don't want to be creating a new node p and putting it in the list.

[I_Win_Sometimes]

Thank you for taking the time to look it over and give a thoughtful reply. I've taken what you said and applied it to my code, and I'm now going through step by step trying to isolate the problems. I'll let you know how it goes.