CS 100, Summer 2001
Tuesday, 7/10
Lecture 8
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Announcements: 
+ Exercise 5 due 7/11
+ PRELIM 1 results (avg 53, good!)
+ Assignment 2 results (avg 84/100!)
+ drop deadline is Friday
+ will post grades soon; please check them over
+ reading: Savitch 5.5
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Topics:
+ methods
+ scope
+ intro to OOP (object oriented programming)
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+ Methods 
- philosophy: eliminate redundancy and unnecessary repetition,
  division of labor, code reuse later
- Example: song lyrics (when chorus is repeated, abbreviate by just
  writing "Chorus".)
  - "Floating" by the Moody Blues
- two kinds: perform action, return value (or both)
- examples:
  - "open the door" method (no input; action: opening door; no output)
  - "read this book" method (input: book, action: reading; no output)
  - "take this money and buy my groceries for me" method: 
     (input: money, grocery list; action: purchasing, transport back; 
     output: groceries (and change!))
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+ syntax:
 public static returntype name(parameters) 
 {
      statements;
      return value; // unless the method is void
 }
+ Java is strongly typed, so 'parameters' is composed of series of 
  inputs with this form:
      type var1, type var2, ..., type varn 
EXAMPLE: Methods.java
EXAMPLE: NoMethods.java (same thing without methods)

+ return keyword/statement (ends processing of method)
EXAMPLE: TensComplement.java
- note method output is NOT the same as printing something out
- method is a little box: 
  you give it something, something else comes back out

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+ Scope: 
- what portion of the code is visible to another portion ("within scope")
- think visibility -- can a portion of code see a particular variable? 
- look for braces { } (these are like "walls")
  - variables declared inside the { } can only be seen by other
    statements inside the same set of braces 
- for classes, you will see that classes can be used from 
  other classes when the classes are located in the same project
  - actually, you have already seen this (SavitchIn.java)
EXAMPLE: scope.java
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OOP
+ grapes: want to do stuff with them
  - wash the bunch of grapes
  - eat grapes
  - make wine! (no method for this. Some of us are under 21.)

EXAMPLE: BunchOfGrapesNoObjects.java
  - main calls different BunchOfGrapes methods to test them.
  - There are two ways to write general methods for the bunches
    of grapes:
    1) add a parameter indicating which bunch, and use switch
    2) write separate methods for each bunch of grapes
  - Big drawbacks!
    1) Lots of repetition
    2) Have to change every method each time I want another
       bunch of grapes
    3) Wastes programmer time
    4) Error-prone
  - Imagine adding checks to eatGrape() to make sure that there 
    are > 0 grapes available.

Now, see BunchOfGrapes.java (and GrapesTester.java)
  - All of the information needed for a single bunch of grapes
    is included in BunchOfGrapes.java, and it is much shorter.
  - Can easily create new bunches of grapes - no need to change
    BunchOfGrapes.java!
 
+ OOP philosophy: group related information together 
+ doesn't add new functionality, but makes a LOT of things easier!
+ combine data (variables) and functions (methods) together
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Bring your questions tomorrow!  OOP is fun, but it's a big concept to
wrap your head around.  We'll talk about this as much as you like. 
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Pick up Exercise 5 handout.