CSC152 2005F, Class 04: An Introduction to Java (1)

Admin:
* New class member: Tom; senior Biol. Chem / Econ major (prewealth) who believes computers are useful.  We expect to prove him wrong.
* Convo tomorrow.  Extra credit.  Why go?
* Today's lab continues on Friday
* Questions on yesterday's lab?
* New Web site questions?

Overview:
* Review
* High-level discussion of Java
* Questions on the readings
* Lab!

Yesterday's lab:
* Emacs doesn't believe in dialog boxes

Review: What is an Object-Oriented Language?
* An OOL is a language that uses objects as the primary building blocks of programs
* Objects are described by classes
* Each object has some information (aka fields, data, attributes)
  and ways to process that information (aka methods, functions, procedures)

Example:
* "Numbers" is a class
  * Each number has a value (field, more or less)
  * Each number can be printed on the screen
  * Each number can be added to, subtracted from, multiplied by, etc. other similar kinds of numbers
* "Rational Numbers" is a class closely related to numbers
  * Every rational number is a number
  * The "value" of a rational number is traditionally specified with two parts, a numerator and denominator
  * To add two rational numbers (creating a new rational number), a/b and c/d = (ad + bc)/bd

Key Tasks in Object-Oriented Languages
* Specify classes:
  * Each class goes in a file named CLASS.java (e.g., Rational.java)
  * Classes begin with the words
  	PROTECTION class NAMEOFCLASS
	{
	} 
	public class Rational
	{
	  int numerator;
	  int denominator;
	  public Rational add(Rational other) { ... }
	}
* Instantiate objects:
  new NAMEOFCLASS ( PARAMETERS )
  E.g., new Rational(1,2) ; new Rational("1/2")

Typical programs:
  * Describe names
  * Create objects
  * Tell objects to do things
* Tell objects to do something (invoke methods):
  NAMEOFOBJECT.NAMEOFMETHOD(PARAMS)
  screen.display(rat.toString())
* Encapsulate/protect:
  Later
* Begin:
  Create a special kind of class (Sam calls it a "main class")
  That class has a method called "main"
  "main" must look as follows:

  public static void main(String[] args)
    throws Exception
  {
    STUFFYOUWANTTODO
  }
* Inherit:
* Polymorphism: