CS 100, Summer 2001
Tuesday, 7/17
Lecture 12
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Announcements: 
+ Assignment 4 due 7/19
+ Prelim 2 on 7/20 
+ reading: Savitch 6.2,
  Chapman 2.3, 2.4, 2.5, 2.7, 2.0
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Topic:
+ arrays
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+ Online submission: did it work?
  - Allows us to run our own tests on your code
+ Assignment 4
  - update to Spaceship.java
  - how to scroll output window: see instructions on Assignments page
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+ Summary from last time
  - encapsulation (remaining questions?)
  - graphics
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+ Graphics
  - WindowDestroyer - use Savitch's class, if you like
  - paint() takes in a Graphics object, g
  - what does it look like?  you don't need to know!
    (remember encapsulation?)
  - just use it to call graphics methods
+ to explicitly force a redraw (e.g., if you've updated some 
  variables that will cause a change in the image), call
  repaint().  This will do some stuff and then call your paint().
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+ Arrays
  - new kind of object: a group of objects that are all the same type
  - these are numbered from 0 up
  - EXAMPLE: ArrayOfTemperatures.java
    - want to read in 7 temperatures, output the average,
      and indicate which ones are above and below average
    - could have 7 doubles to store them, but this gets impractical
      if we want to increase the number of days we're analyzing
    - solution: use an array!
  - syntax for array declaration
      type[] name = new type[howMany];

  - Three uses for square brackets:
    1. To indicate a type, e.g.
        int[] myArray;
    2. To indicate the size of an array, e.g.
        myArray = new int[26];
    3. To index an element of an array, e.g.
        int x = myArray[5];

  - note the "new"! Arrays are objects.  This means they can have
    variables and methods.  A useful one is:
      array.length
    stores how long the variable is. (Compare with String.length())
  - Java keeps track of array bounds for you
    - it will "throw an exception" if you use an invalid index,
      for example:
        array[-1]
        array[24387534] // if array doesn't have that many elements
    - more about exceptions tomorrow
  - TRY IT YOURSELF: Draw pictures to follow what's happening with the
    arrays in ArrayOfTemperatures.java

EXAMPLE: Spaceship2000.java
- implement the moveFormation() method as an example of how to use
  arrays
- solution is posted on the Syllabus page for today
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PICK UP graded Exercise 7, download Exercise 8 from webpage