Question

for (String msg : messages) {
    System.out.println(msg);
}

Say that messages is a properly initialized circular, doubly linked list that has no head or end pointer (reference). That is, it just has a current node pointer. My question simply is what exactly is the enhanced for loop doing for each iteration. If necessary, I have an interface that I can post for this special type of ADT that messages is.

Here is the iterator:

import java.util.*;
public class LinkedCircularSequenceIterator<E> implements Iterator<E> {
     private DblListnode<E> curr;
     private int itemsLeft;

  public LinkedCircularSequenceIterator(DblListnode<E> curr, int numItems) {
    this.curr = curr;
    this.itemsLeft = numItems;
  }

  public boolean hasNext() {
    return itemsLeft > 1;
  }

  public E next() {
    if(!hasNext()) {
        throw new NoSuchElementException();
    }
    curr = curr.getNext();
    itemsLeft--;

    return curr.getPrev().getData();
  }

  public void remove() {
    throw new UnsupportedOperationException();
  }
}

Answer 1

It should be doing something like

Iterator<Message> iter = messages.iterator();
while (iter.hasNext()){
    msg=iter.next().toString();
    System.out.println(msg);
}