CSC297.Java, Class 17: Even More Lists!

Admin:
* We are not doing BishopD's new assignment.
* What did you learn from the Java list class?
* How did your homework go?  
* New homework: Read about the Java collections framework at
  http://java.sun.com/j2se/1.4.2/docs/api/
* New homework: Try implementing lists with vectors and the "store it backwards" strategy.  We *will* look at your code on Wednesday.
* Announcement: Two talks
  * Thursday, noon, 2413, Shaka McGlotten '97, "Gender, Sexuality, and other Stuff in Online Communities"
  * Friday, noon, 2413, Joshua Shaw Vickery '02, "Real-World Java Programming"
 
Overview:
* java.util.List
* Vector-based-lists, revisited.
* Extending those lists.
* Implementing mutable lists with nodes.
* Variations.

/java.util.List/
* What methods are in java.util.List that are not in MutableList?
  * contains(Object)
  * list-ref
  * index-of
  * last-index-of
  * remove
  * sublist
  * many more
* Which of these would we want to include?
  * The ones listed explicitly above

/Vector-based Lists/
* Why would you ever want removeFirst to return something?
	try {
	  while (obj = stuff.removeFirst()) {
	    // Process obj
	    ...
	  } // while
 	} // try
	catch (Exception e) {
	  // Done removing and processing all the elements
	} // catch
* Morals:
  * Many things you want to do are done in the API.
  * There are still some advantages to figuring out how to do things by hand.
  * Be careful about dealing with the length of a vector.
* Questions:
  * About how many steps does it take to add something to the front of a Scheme list of length 100?  One step: Cons the new thing to the list.
  * About how many steps does it take to add something to the back of a Scheme list of length 100?   Approximately 200: 100 to cdr through the list until we hit the end, 100 to build up the new list of 101 elements.
  * About how many steps does it take to add something to the front of a VectorBasedList of length 100? About 100.
  * About how many steps does it take to add something to the back of a VectorBasedList of length 100? Sorry, this operation is not supported.
  * About how many steps does it take to delete the first element of a Scheme list of length 100? One step.
  * About how many steps does it take to delete the first element of a Vector-based list of length 100? 100 steps.
  * What does this suggest about our implementation?  It sucks.

/Improving VectorBasedLists/
* Suppose we only have the few operations we started with (particularly addToFront and deleteFirst as the only mutators).
* Can we make our VectorBasedLists more efficient?
* Try funky things with "wrapping around". [JLW] = [JWells]
* Store the list in reverse order.

/Improving Lists in General/
* What if we want to efficiently add to and remove from both ends of the list?
* Reflection: What did we do last week to make the ImmutableLists more efficient?
* Don't use Vectors or arrays.  Instead, use Pairs/Cons Cells
* Idea: We keep track of the cons cell of the front of the list and the cons cell of the back of the list.
* To add to the front, shove another cons cell on and update our knowledge.
* To add to the back, shove another cons cell on and upate our knowledge.