TAO of Java, Class 2: More Java Basics

Overview of Object-Oriented Programming
Your First Java Program
Running Java in the MathLAN
More on Input and Output in Java

Object-Oriented Programming: Greek Philosophy in Action
* Almost everything in the progrm is "an object"
* Objects combine data and functionality
* Objects are built from "templates" called "classes"

Example: Fractions (Also called Rationals)
* Every fraction has a numerator and a denominator
* Different fractions may have different numerators and
  denominators
* You may expect to divide two fractions
  * Fraction A: Divide yourself by fraction B
  * Thingy: Divide fraction A by fraction B
* Similarly, you may expect to multiply, add, subtract, ...
* Also
  * Express as a real number
  * Simplify

Creating a fraction:
* First, describe the generalities (see above)
* Next, say "I want to create the fraction 1/2"; it gets
  all of the properties described above.

public class Fraction 
{
  int numerator;
  int denominator;

  Fraction multiply(Fraction other) 
  {
    // Instructions for multiplying
  } // multiply(Fraction)
} // class Fraction

Generically:

FUNCTION-DEFN:
  RETURN_TYPE FUNCTION_NAME(LIST-OF-PARAMETRS)
  {
    INSTRUCTIONS
  }

PARAMETR:
  TYPE PARAMETER_NAME

How to make a new fraction

  Fraction oneHalf = new Fraction(1,2);

"new" says to create a new object; if it's not there, the
compiler simply looks for a function with the given name.

---

Second key aspect of object-oriented programming:
  "Inheritance"

You can design new classes based on other classes,
without duplicating the stuff from the original class

A library book is a book and adds the following 
* Data: Call number, Checkout status, ...
* Capabilitieis: borrow, return, ...

---

Third key aspect of object-oriented programming:
  "Polymorphism"

If you've written a procedure that deals with one kind
of object, it automatically deals with all "similar"
objects

---

Final key aspect of object-oriented programming:
  "Encapsulation"

Hide the innards of the object from the outside world.
The outside world simply has access to the functionality
we choose to reveal

-----