CSC152 2004F, Class 42: Vectors

Admin:
* Yay!  Everyone is here on time!
* No alumna talk today!
* Math/CS lunch!
* Evil thieves stole projectors and other stuff

Overview:
* About vectors
* Testing!

/Today's Goals/

* Learn more about this very useful class.
* Think more about how we read documentation.
* Think more about how we write tests.

/Four Key Aspects of ADTs/

* Philosophy
  * Vectors are arrays that can expand when you need more room
  * Vectors provide lots of related methods that programmers normally use
    * remove(int index)
      * Remove the thing at position index, shift everything left
      * Shrinks!
    * add(int index, Object value)
      * Add something at position index, shift everything right
      * Expands!
      * What is the running time?  Probably O(n)
* Methods
  * Array-like
    * set(int index, Object value)
      * pre: Vector must be nonempty
      * pre: 0 <= index < size()
    * get(int index)
      * pre: 0 <= index < size()
    * size()
    * "construct"
    * setSize(int newSize)
  * Design question: How should they automatically expand?
* Implementation
  * Have a field that contains an array
  * If you need more room, make a new array and copy the data over
* Application

/Learning Vector Methods Through Testing/

* Detour: How can you call a new method from a main?
  * Strategy one: Create an object in the appropriate class
  * Strategy two: Designate the method as something that does not need an object to associate itself with (only needs parameters)
    * We call such methods "class methods" or "static methods"
    * Such methods cannot access most fields of the class
    * Static methods are traditionally accessed as ClassName.methodName(params)
* The initial size of vectors is: 0
* If you try to set the initial element of a vector without changing the size: It crashes (throws an exception)
* set and get behave the way we expect

Some programmers (or philosophers of programming) advocate writing the tests for your ADTs before you implement your ADTs!
* Test-driven development

Coming Wednesday: SORTING!  You do not need to study any of this in advance
* Merge sort
* Bubble sort 
* Insertion sort
* Heap sort!
* Selection sort
* Quicksort
* Bucket sort
* Radix sort

/Notes for the World Folks/

public class ExceptionTester
{
	public static void main(String[] args)
		throws Exception
	{
		try {
			throw new NotAVerb();
		}
		catch (Exception e) {
			pen.println("OOh ... " + e.toString();
		}
	}
} // 

You walk into MathLAN.  You see: leigh, brad, computer1, computer2, ... chair1, chair2, angeline, invisibleprojector, ...
Action: Pick up computer
Sorry, nothing here is called computer.  Try computer1 or computer 2.
Action: Pick up computer1
Sorry, it is too heavy.
Action: Yell at computer1
It explodes.  You are now dead.  Please play again.