Help in understanding the add method particularly addBefore of linkedList Implementation

[Sandeep Dharwar]

Can someone walk me through the logic of the addBefore method in 2 cases when the list is empty and when there are several elements in the list. I have included the necessary code required for the understanding of this operation.

   private transient Entry<E> header = new Entry<E>(null, null, null); 

    public boolean add(E e) {
    addBefore(e, header);
    return true;
    }

 private static class Entry<E> {
        E element;
        Entry<E> next;
        Entry<E> previous;
        Entry(E element, Entry<E> next, Entry<E> previous) {
        this.element = element;
        this.next = next;
        this.previous = previous;
        }
    }

private Entry<E> addBefore(E e, Entry<E> entry) {
        Entry<E> newEntry = new Entry<E>(e, entry, entry.previous);
        newEntry.previous.next = newEntry;
        newEntry.next.previous = newEntry;
        size++;
        modCount++;
        return newEntry;
    }

[Edit = CR]Have removed the double-spacing and the line numbers from the code; they both make it more difficult to read.[/edit]

Thanks in advance.

[Winston Gutkowski]

Sandeep Dharwar wrote:Can someone walk me through the logic of the addBefore method in 2 cases when the list is empty and when there are several elements in the list. I have included the necessary code required for the understanding of this operation.

My suggestion would be to draw it out on a piece of paper, maybe something like:

           +-------+       +-------+
       prev|       |   prev|       |
  ...<-----|   A   |<------|   B   |<----- ...
           |       |next   |       |next
  ...----->|       |------>|       |-----> ...
           +-------+       +-------+

and now think about (and write down) the operations needed to add a new node before B.

Winston