cs2340: Objects and Design: Some OO History and Object Theory

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cs2340 Objects and Design Some OO History and
Object Theory

• Spring 2007

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Object Theory

• Read Budd book chapters on-line
• Just using an Object-Oriented language does not
  mean you truly think in objects!
• Side Note Languages are tools, one is not
  better than another in a general sense.

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Sending Flowers (Procedural)
What do I need to do? What data do I need?
Chris
Robin
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Sending Flowers (OO)
Arranger
Goal Send Flowers to Robin
Goal Turn Raw Flowers into an arrangement
Florist
Chris
Goal Create Flowers
Grower
Goal Satisfy Customer
Wholesaler
Goal Provide Fresh Flowers
Robin
DeliveryPerson
Goal Deliver Flowers to Robin
Adapted from Budd
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What characteristics do we see?
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Object-Oriented Mantra

• Objects do the work. The work is done in instance
  methods in the appropriate class. Good objects
  have clear, cohesive responsibilities and clear
  focused interfaces.

• Budd OOP is structured as a community of
  interacting agents called objects. Each object
  has a role to play. Each object provides a
  service or performs an action used by other
  members of the community.

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So What is an Object?
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An Organizational Hierarchy

• An application a set of interacting objects
• An object an implementation of one or more
  roles
• A role a set of related responsibilities
• A responsibility an obligation to perform a
  task or know information
• A collaboration an interaction of objects or
  roles (or both)
• A contract an agreement outlining the terms of
  a collaboration

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Sending Flowers (OO)
Arranger
Goal Send Flowers to Robin
Goal Turn Raw Flowers into an arrangement
Florist
Chris
Goal Create Flowers
Grower
Goal Satisfy Customer
Wholesaler
Goal Provide Fresh Flowers
Robin
DeliveryPerson
Goal Deliver Flowers to Robin
Adapted from Budd
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Contrasting Object vs. Procedural Thinking

• Design the software for the Mars Rover.

Verb-Oriented vs. Noun-Oriented
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Start of the Story Late 60's and Early 70's

• Windows are made of glass, mice are undesirable
  rodents
• Good programming Structured programming
• Verb-oriented
• Punch-cards, teletype terminals

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Howd we get from there to here?

• How did we move from structured to
  object-oriented?
• Key ideas
• Master-drawings in Sketchpad
• Simulation objects in Simula
• Alan Kay and a desire to make software better
• More robust, more maintainable, more scalable

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Birth of Objects, 1 of 2

• Ivan Sutherland's Sketchpad, 1963

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Birth of Objects, 2 of 2

• Simula
• Simulation programming language from Norway, 1966
  (Kristen Nygaard Ole-Johan Dahl)
• Define an activity which can be instantiated as
  processes
• Each process has it own data and behavior
• In real world, objects don't mess with each
  others' internals directly
• (Simulated) Multi-processing
• No Universal Scheduler in the Real World

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Alan Kay

• U. Utah PhD student in 1966
• Read Sketchpad, Ported Simula
• Saw objects as the future of computer science
• His dissertation Flex, an object-oriented
  personal computer
• A personal computer was a radical idea then
• How radical?

"There is no reason anyone would want a computer
in their home." (Ken Olsen, Digital Equipment
Corp, 1977)
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OO History

• Sketchpad Ivan Sutherland (1963)
• Simula Kristen Nygaard (1967)
• Alan Kay Dynabook (1968)

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OOP Term Review

• Class/Object
• Instance
• Message
• Receiver
• Class Hierarchy
• Inheritance
• Overriding/Overloading

• Polymorphism
• Encapsulation
• Abstraction
• Information Hiding