SUNY Geneseo Department of Computer Science

Algorithm Design with Objects

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CSci 141, Spring 2005
Prof. Doug Baldwin

Misc

Hand out Lab 2

Chapter 2

Abstraction

Value-producing algorithms vs side-effect producing algorithms

Subclasses, e.g., drawing robots, show different things you can do

Preconditions and postconditions, contract between clients and implementors re interface to algorithm

Implementor deals with "dirty bits" inside algorithm, client should see clean, simple interface

Examples of object-oriented concepts

[16 Chess Pieces on a 4-by-4 Board]

What concepts from the reading were there in this game?

Preconditions: initial set-up
- Also for moving (can't move through occupied square, etc)
Postconditions: check mate
- And for moving (taken pieces, positions change)
Classes & subclasses
- "Piece" is a class
  - Have color
  - All can move
    - But not if it goes off board
    - If move reaches another piece, it's captured
  - "Captured" vs "not captured"
- "Pawn," "knight," etc. are subclasses
  - How they move
Inheritance: e.g., "color" property
"Board" could also be a class
"Move" is a message
- (Also "castle" in full chess)
"Move" needs information about where to move to - parameter

Theoretical Reasoning about Algorithms

Read Sections 3.1 - 3.3, 3.6