CSC153 2004S, Class 42: Designing List ADTs

Admin:
* About preregistration and the CS major
  * Fall
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      * Algorithms for parsing sentences
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    * Potentically HCI group independent
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    * OS: The program that manages everything on the computer (processes, filesystem, etc.)
    * Architecture: Assembly-language programming, design of hardware (registers, ALU, how addition works, pipelining, etc), 
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Overview:
* What is a list, revisited?
* What operations should lists provide?
* What interesting variants are there?
* Implementation Friday (arrays) and Monday (pairs)

/Philosophies of Lists/

* Like Scheme lists (series of nodes/pairs): 4
  * Sounds like an implementation rather than an ADT
  * Doubly-linked lists are a variant implementation
  * Circularly-linked lists are another variant implementation
* Indexed collection: 2
  * Sounds like an array
* I didn't get around to it: 1 
  * Sounds wrong
* Sam's theory: A list is a Collection you can iterate but may not have indexed access to
  * Generalized list: The order of iteration is up to the implementer
  * Ordered list: The client gets some explicit control over the order
  * Sorted list: The elements are iterated "in order" from smallest to largest
* Hierarchy
  * Every ordered list is a generalized list
  * Every sorted list is a generalized list
  * Sorted lists are not ordered
  * Ordered lists are not sorted

Observation:
* We can generalize some of the Node methods by providing an abstract "position"

What methods do your books provide for lists?
* construct the empty list - GL
* boolean isEmpty() - GL
* addAtFront(Object newFront) - OL
* addAtEnd(Object newFront) - OL
* swapElement(Position here, Position there) - OL
* remove(Position here) - GL
* getNextItem() - GL
  * Assumption: implicit position
* getAtIndex(int index) - Array
* Object get(Position here) - GL
* Position first() - GL
* Position last() - GL
* add(Object addme) - GL
* addAfter(Position here, Object addme) - OL
* addBefore(Position here, Object addme) - OL
* boolean contains(Object value) - Set
* Object replaceAt(Position here, Object replacement) -  [returns replaced]
* boolean isFirst(Position here) - GL
* boolean isLast(Position here) - GL
* Position prev(Position here) - GL
* Position next(Position here) - GL
* int length() - GL
* void clear() - GL
* Position find(Object findme)
* remove(Object removeme) - GL [one or all copies of an object]

The "instanceof" operation
  if (obj instanceof OrderedList) 
    ((OrderedList) obj).addAtFront(whatever);
  else
    obj.add(whatever);

  Object.getclass()

Design decision: Should we have implicit positions?

/**
 * Add an element to the list.
 *
 * Postconditions:
 *   All positions in the list are now invalidated.
 */
public void add(Object addme);