Lecture of 5 January 1996

• Hand out syllabus
• Take Initial Class Roll
• Note and Show Texts
• Other Materials
  • Usenet newsgroup comp.object
  • The comp.object Object-Orientation FAQ
• Programming Languages and Tools
  • C++ Programming Language
  • Dylan Programming Language
  • (Objective-C)
• Grading criteria -- see syllabus
• Workload: (less that CDA 3101, more than COP 3530)
• Reading Assignment: Budd ppg. 1-35
• Homework Assignment:
• Practice vs. Science (techne)
  • Art of Computer Programming, D. Knuth
  • Science of Computer Programming, D. Gries
• To some of you, many of the concepts and techniques presented in the class will seem familiar. To others, they will be new. The class does not espouse the one true way of programming. It is dangerous to invest too much belief in any method or activity. The goal of the class is to provide you with a set of tools for carrying out object-oriented design of software and implementation using object-oriented programming techniques.

Story of the Vasa

• 1625: King Gustav of Sweden commissions construction of a new flagship, the Vasa.
• Hendrick Hybertszoon (master shipwright from Holland) is selected to build it.
• No written specifications
• Shipbuilder assumes ship will be 108 feet in length. After first review, King Gustav requests a 135 foot ship. Timber is added to make the ship 120 feet.
• While on vacation, King Gustav finds out that the Danish king is building a ship with three gun decks. He asks that a third gundeck be added to the two already on the Vasa. 50 brass 24-lb cannons (at one ton each) will be added.
• Stability tests are conducted (involving 30 sailors who run from one side of the ship to the other). The ship appears to be stable.
• On a Sunday in August 1628, the Vasa sets sail. One mile from harbor a wind gust catches the main sail and the ship overturns and immediately sinks.
• The Vasa was later brought up from the briny deep at greater cost than was expended in her manufacture.

Parallels between Shipbuilding in the 1600's and Software in the 1990's

• Shipbuilding in the 1600's was a craft based on engineering practice.
• Specifications for ships were ad hoc and usually verbally communicated.
• Designs for ships were inadequate to insure the finished product would satisfy the needs of its users.
• The full implications of changes to the design were not always understood.
• Too much time was wasted carving decorative sculpture prior to determining if the ship would sail.
• Success breeds failure. Those who succeeded in building small ships would believe they knew how to do it even though they had no idea of the fundamental physical principles involved.
• Shipwrights in the 1600's (one in particular) did not know how to say ``no'' to customers.

Implications:

1. Systems may last longer than we think (sometimes hundreds of years).
2. Maintenance costs may exceed the original development cost.
3. We can examine, in minute detail, components of systems we have built decades or even centuries later.

Thinking Object-Oriented

• What is Object-Oriented Programming?
• Why is it popular?
  • Offered up as a way to increase productivity
  • Offers a way of programming that is similar to lines of though in other problem domains.
• OOP as a new paradigm (Any example or model)

  par-a-digm n 1. A list of all the inflectional forms of a word taken as an illustrative example of the conjugation or declension to which it belongs. 2. Any example or model. [Latin paradigma, from Greek paradeigma, model, from paradeiknunai, to compare, exhibit.]

• Sapir-Whorf Hypothesis: As put by Marshal McLuhan, the medium is the message. The language or medium or form in which an idea is expressed determines the nature of the thought expressed. Lakhoff's recently touted book, Women, Fire, and Dangerous Things summarizes a view of categorization known as prototype theory that shows the way languages reflect categorizations that are culturally shared but may differ radically from group to group in large part due to linguistic convention.

  The marked effect that computer languages have on the programs we generate cannot be denied.

• Imperative Programming
  • State (ep/ip pair)
  • Assignment
  • Control
• Properties of Object-Oriented Programming
  • All entities upon which computation can be performed are objects.
  • Objects are unique, that is, they are distinct from each other.
  • Objects perform computation by either
    • making request of each other through messages, or
    • having requests for computation brokered through some medium (generic function approach)
  • Each objects has its own state (which may consist of other objects)
  • Each object belongs to some class which denotes the collection of all objects sharing belonging to some category
  • Classes of objects share common behavior
  • Classes are organized into one or more tree structures known as an inheritance hierarchy.