SUNY Geneseo Department of Computer Science

Object Oriented Programming Concepts, Part 2

Previous Lecture

Misc

CodeWarrior problems with robot

• Seems to be a CodeWarrior/Mac Java misfeature
• We'll probably move to ProjectBuilder, with intro to it in tomorrow's lab
• CodeWarrior works fine on PC's

CS Learning Center

• MTWR evenings (7:00 - 8:30 or 7:00 - 9:30)
• In printer room between labs

Questions?

Turn in labs today -- any time, preferably into my hand

Intro to Design

(Chapter 2)

Expressions as algorithms for computing values

Values -- objects can contain them in member variables

Mini-Assignment:

Design an algorithm for the robot described in the book that makes the robot move forward until it comes to a wall.

Preconditions: no obstacles between robot and the wall

Version 1:

• Command robot to walk,
• When it comes to a wall it stops

Version 2:

• Tell robot to take a step, checking as you do that robot isn't at wall
• (When robot comes to wall, it stops)

Version 3:

    loop while robot can move
        move

Version 4, finally, is Java Code

Postcondition: robot is on tile before wall, still facing in original direction

What does this exemplify from the reading?

• Messages, object, (class)
• Algorithm
  • Steps = check to move, move
  • i.e., messages to robot
• Pseudocode
• Abstraction
  • Messages
  • Pseudocode refinements (such "stepwise refinement" is a really good way to develop any program or algorithm)

Next

Introduction to Theory

Consider making change using the fewest coins:

• Start with highest-valued coin,
• Give as many of that coin as you can
• Repeat with lower valued coins

Suppose there was 4-cent coin, 8 cents change

• The "greedy" algorithm doesn't work! So now how do you know there isn't some obscure case where it doesn't work with standard US currency?

Read Sections 3.1 - 3.3 and 3.5

Next Lecture