Linked List Manipulation

[chrisdb89]

I have already posted this at forums.sun.com, however as of yet nobody has been able to help me. If someone replies, I shall let you know so that the same things aren't being said more than once!

I'm having trouble with a final method which I'm trying to implement. I am using the following interface:

public interface ILinkedList {
 
	public abstract Object getHead();
 
	public abstract ILinkedList getTail();
 
	public abstract void setHead(Object head);
 
	public abstract void setTail(ILinkedList tail);
 
}

And have the following two classes:

public class LinkedList implements ILinkedList {
 
	private Object head;
	private ILinkedList tail;
 
	public Object getHead() {
		return head;
	}
 
	public ILinkedList getTail() {
		return tail;
	}
 
	public void setHead(Object head) {
		this.head = head;
	}
 
	public void setTail(ILinkedList tail) {
		this.tail = tail;
	}
 
	public LinkedList(Object head, ILinkedList tail) {
		this.head = head;
		this.tail = tail;
	}
 
}

and

public class ListManipulation {
 
	/*
	 * Return a string representing the list as a comma-separated list of values
	 * enclosed in [...] . Use the toString() method of the individual list
	 * entries to print the values.
	 * 
	 * An example of an iterative method. The complexity of this method comes
	 * from the fact that a comma-separated list of n objects has n-1 commas
	 * unless n = 0. So there needs to be a special case.
	 */
	public static String convertToString(ILinkedList l) {
		/*
		 * build up the result in a StringBuffer rather than a String for
		 * efficiency
		 */
		StringBuffer s = new StringBuffer("[");
		if (l != null) {
			/*
			 * deal with the first element specially, as there is no comma
			 * before it
			 */
			s.append(l.getHead().toString());
			l = l.getTail();
			/*
			 * Now things are regular and we go into a loop to run down the rest
			 * of the LL printing each item preceded by a comma
			 */
			while (l != null) {
				s.append(", " + l.getHead().toString());
				l = l.getTail();
			}
		}
		/* Finally close the bracket and convert to a String */
		s.append("]");
		return s.toString();
	}
 
	/*
	 * return a new list consisting of the elements of l1, followed by those of
	 * l2. The result may share nodes with l2 if this is useful
	 * 
	 * implement recursively
	 */
	public static ILinkedList append(ILinkedList l1, ILinkedList l2) {
 
		while (l2 != null) {
			l1.setTail(l2);
			l2 = l2.getTail();
		}
		// l2 is null and so new list is just l1
		return l1;
 
	}
}

It is the append method which I'm unsure of. I understand that if I have two linked lists (written in shorthand as) [1,2,3] & [4,5], that I want to take the head of the second list (4) and append it to the tail of the first list (2,3) - I have to implement this recursively. What I have at the moment in the append method, I believe will make the first list [1,4], as I think it will replace the current tail with the head of the second list.

Does anybody have any suggestions as to how I would otherwise implement this to append the second list onto the first? I tried l1.setTail(l2.getHead()); but the interface doesn't allow this (and the interface cannot be changed).

Thank you to anybody who is able to suggest anything :)
Christopher

[xcallmejudasx]

I think you may be over complicating this(or I'm way under complicating it). Why don't you just the replace method of StringBuffer to replace "]" with ", "+l2.getHead().toString() and when l2.getTail() == null s.append("]")

Like I said I may be way over simplifying this and this might not even be possible but it's an easy solution that logically would work.

[chrisdb89]

I think you may be over complicating this(or I'm way under complicating it). Why don't you just the replace method of StringBuffer to replace "]" with ", "+l2.getHead().toString() and when l2.getTail() == null s.append("]")

Like I said I may be way over simplifying this and this might not even be possible but it's an easy solution that logically would work.

Thank you for replying.

I was given a list of methods which I had to implement, and so from that I think that l2 must only come into the equation when dealing with the append method. I am also unable to change the interface, or the LinkedList Class, as these were supplied to us.

[chrisdb89]

I received help at the other forum, which solved my problem.

Thank you for your help, though :)

Christopher