SUNY Geneseo Department of Computer Science

Object Oriented Programming Concepts

Previous Lecture

Misc

Missing appendix for book

Course e-mail list has a different name:

• csci141-spr04-l@geneseo.edu

Questions?

If "method" is executed by an object, what about "main"?

• "Static" methods aren't associated with objects
• Executed by "the computer"

Reading Summary

Chapter 2

Program, implementor and client

• Client: gives preconditions
• Implementor: works with preconditions to establish postconditions

Robot example -- e/g., drawing squares

Abstraction

• Helps you do tasks

Algorithms that are series of steps

Classes, methods, messages

• How to use messages in algorithms

Algorithms produce either side-effects or values

Abstraction also allows hiding values (member variables) as well as actions

An Example Abstraction

Cell phones

Software is very complicated

• Developers need to think abstractly
• Think about details of some parts while ignoring details of other parts

Another example:

"for all real numbers, x, x+1 > x"

• "x" is abstraction
• Mathematics is probably our best-developed abstract system

Mini-Chess

An example object oriented system

Play a game

What object oriented concepts did you notice in this game?

• Abstraction, e.g., in directions to pieces (aka messages)
• Objects (16 pieces, board)
• Classes (pawn, king, knight, etc)
• Subclasses (pawn, king, etc. are variations on "chess piece")
  • Maybe also black pawn vs red pawn
• Or could think of color as "state", also position, captured or not
  • Often represented in member variables
  • "Checkmate" as a piece of board's state?
• Method -- Algorithm (what pieces did)
• Messages (commands from players)
• Parameters (information about where to move)
• Objects have names
• Side effects (pieces changed position, leaving game)
• Preconditions (no move can put own king in check)
• Postconditions (pieces having new positions, pieces have been captured)

Next

Theory

Read 3.1 - 3.3, 3.5, 3.6

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