CSC297.Java 2003F, Class 21: List Cursors/Iterators

Admin:
* Have a great break!
* Sam will try to write during break.
* Homework for break:
  (1) Finish implementing YDLLItertaor
  (2) Implement some sorting algorithm on doubly-linked lists.

Overview:
* What methods did you come up with for iterators?
* How will we implement those methods?

Reminder:
* Lists are collections of values that can be "iterated"
* "Iterate" means to look at each value in the collection in turn
* There are situations in which we iterate the list "in parallel"
* Hence, we need separate "List Iterators"

Basic Iterator Options:
* Create a new iterator at the start of the list.
* Advance the iterator to the next element.
* Get the current value.
* Retreat the iterator to the previous element (perhaps)
* Delete the thing the iterator currently refers to and advance the iterator to the next element.
* Advance the iterator to a particular value
* Insert before
* Insert after
* Replace

As an alternative to iterators, we can have fun higher-order procedures (map, fold, ...).

The jwells operator, impelemented

  List jwells(List lst, BinaryProcedure binproc) {
    List result = new List();
    Iterator left = lst.newIterator();
    Iterator right = lst.newIterator();
    right.advance();
    while (right.isValid()) {
      result.addToEnd(binproc.applyTo(left.current(), right.current()));
      left.advance();
      right.advance();
    }
    return result;
  } // jwell(List, BinaryProcedure)