CSC153, Class 29: An Introduction to Java

Overview:
* Object-oriented programming

Notes:
* Read lab J2 for tomorrow.
* I went to an interesting conference.  I'll describe a problem
  another computer scientist at that conference told me about.
  (The problem has nothing to do with the focus of the conference, 
  but it's fun anyway.)
* Warning: I wrote our Java stuff five years ago.  Java has 
  changed.  So have some of my opinions on how best to teach 
  this stuff.
* Today is mostly lecture, little lab.
* Are there questions on exam 2?

Do I need to rewrite type preconditions?
  No

How should I document Curried procedures?
  Just like they're normal proceduresa

Should I document my helper procedures?
  At least a little for every one.
  Internal helpers only need a sentence or two.
  External helpers need six P's.

Discussion of various questions

Bring more questions tomorrow.

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Java is an "Object Oriented" language

What does it mean to be object-oriented?
* Basic unit of the language is "the object"
* What is an object?
  A collection of values and things you can do with those
    values
  E.g., a book
    Values:
      Number of pages: 334
      Author(s): Ken Arnold and James Gosling
      Title: The Java Programming Language
      Contents: ...
      Adjectives: ...
      ISBN: ...
      Many more ...
    Capabilities:
      read, given a reader
      burn, given a match
      openTo(pagenumber)
      getIndex returns an index that supports
        lookupPageNumber(topic)
  Note: Be careful on your abstractions so that they can
    handle appropraite concrete thingys.
* What else goes in an object-oriented language?
* Procedures?  Not in a pure OO language.
* Classes abstract commonalities between objects
  Every book has author, title, ...
  Every book can do x, y, and z ...
  A lot like a higher-order procedure: Can be used with
   many things that take the same form.
* What else goes in an object-oriented language? (other than
  objects and classes)
* Inheritance: You can define new classes based on existing
  classes.
  + E.g., a library book is a book
    + Add values (attributes, fields)
    + Change 'em
    + Change capabilities
    + Add capabilities
* Polymorphism: Many forms
  One procedure can act on many different types of data
* Encapsulation
  You can know *what* an object/class does, but not *how*.

Object-oriented programming is the embodiment of two key
strands of ancient Greek philosophy

* Plato: Everything (object) is an instantaition of a
  an ideal class.
* Aristotle: Hierarchical categorization of nature
  Inheritance