Lecture 6

Object-oriented Programming

Subclasses and inheritance II

MCS 275 Spring 2021
Emily Dumas

Lecture 6: Subclasses and inheritance II

• Quiz 2 is due at Noon tomorrow (Tue Jan 26).
• Project 1 posted. Deadline 6pm CST on Fri Feb 5.
• Project 1 autograder opens on Mon Feb 1.
• Quiz 3 and Worksheet 4 will be lighter (so you can prioritize project work).

Plan

Finish our robot simulation class hierarchy

Discuss more OOP theory & practice

Planned Bot hierarchy

• PatrolBot walks back and forth.
• WanderBot walks about randomly.
• DestructBot sits in one place for a while and then self-destructs.

Planned Bot hierarchy

• PatrolBot walks back and forth.
• WanderBot walks about randomly.
• DestructBot sits in one place for a while and then self-destructs.

Class attributes

Attributes declared in the class definition, outside of any method, are class attributes.

Class attributes are shared by every instance of the class. Often used for constants.

Contrast with the instance attributes we have used thus far (e.g. self.x = 1 in constructor) which exist separately for each instance.

Four pillars of OOP

• Encapsulation - Classes manage their own private, internal state.
• Abstraction - Method calls express intent (independent of implementation).
• Inheritance - Distinct classes can share behavior.
• Polymorphism - Code using a class will also work on its subclasses.

Extending the simulation

Beyond adding more robot types, how might me improve or extend the simulation?

Extending the simulation

Might create a class Arena that manages the list of bots and the space in which they move. Would have a single .update() method that updates all bots.

Arena could have a metthod to render itself as a string for display (or as a PNG, HTML, ...).

Extending the simulation

If we wanted to add robot interaction or movement constraints then the Bot class would need a way to access information about its surroundings.

We might make a parent Arena a required argument to the Bot constructor.

Bot.update() could call methods of Arena to learn about other robots, movement limits, etc.

e.g. in Bot.update():

self.arena.bots_visible_from(self.position,self.sight_range)