CS51 - Spring 2010 - Lecture 16

notes on TP1 style
   - if you find yourself repeating
      - code (even just a few lines): consider using a private method
      - variables: use an array (you didn't know about it yet for TP1)
   - variable scope
      - the only reason you should have a private instance variable is if you use it in more than one method
      - otherwise, make a local variable!
      - I didn't take off points this time, but will next time
   - constants in multiple classes
      - NEVER define the same constant in multiple classes
         - define it in the one where it makes the most sense, and pass as a parameter to others
         - very, very rarely, make it a public constant (come talk to me before you do this :)
   - think about while loops

CS lunch tomorrow

Back to Fibinacci... How do arrays help us?

   private int fib(int n){
      int[] fibArray = new int[n];

      fibArray[0] = 1;
      fibArray[1] = 1;

      for( int i = 2; i < n; i++ ){
         fibArray[i] = fibArray[i-1] + fibArray[i-2];
      }

      return fibArray[n-1];
   }

Show SlidesF09 demo: how can we do this? Hint: use arrays!

Look through SlidesF09 code

Write a function that given an array of ints, returns the largest number in the array
   public int largestNumber(int[] numbers){
      int largest = numbers[0];

      for( int i = 0; i < numbers.length; i++ ){
         if( numbers[i] > largest ){
            largest = numbers[i];
         }
      }
   }

   public int largestNumber(int[] numbers){
      int largest = numbers[0];

      for( int number: numbers ){
         if( number > largest ){
            largest = number;
         }
      }
   }

show TextStat demo
   - String member method: split
      - public String[] split(String splitString);
   - We're going to write the four supporting methods to make this class
      - private String getLongestWord(String[] words)
      - private String getShortestWord(String[] words)
      - private int getNumberOfWords(String[] words)
      - private int getNumberOfCharacters(String[] words)

Show DrawingPanelWithShapeArray demo
   - Note how we can move things around and different objects are "in front" of other objects
   - Hard to get this behavior with recursion
   - We'll do this using arrays:
      - we'll construct an array with some maximum size, call it MAX_OBJECTS
         - private DrawableInterface[] shapes = new DrawableInterface[MAX_OBJECTS];
      - initially, the array will be empty
      - as we add things, add the objects to the array
      - how can we do this?
         - keep an integer (int numShapes) that tells us how many things are in the array so far
   - How do we add a new item?
      - construct the shape
         - figure out the shape from the menu and create a new shape
         - figure out the color from the menu and set color
      - how do we add it to the shapes array?
         - remember, we're using numShapes to keep track of how many items are already in the array
         - set shapes[numShapes] to the new object
         - increment numShapes

Other misc. array things
   - what happens here?
      int[] numbers = new array[10];
      int currentIndex = 0;
      ...
      currentIndex = 10;
      numbers[currentIndex]++;

      ** ArrayOutOfBounds exception
   - what happens here?
      FramedRect[] rects = new FramedRect[10];
      rect[0].move(10, 10);

      ** null pointer exception
      - we've just created an array of FramedRect variables
      - as like any other FramedRect variable, their initial value is null until you assign something to them